Fixes #698.

PrintHelpText now prints to standard output instead of to standard error.
The purpose of this CL is to make it easy for users to grep for matches
otherwise stderr output has to be awkwardly redirectly to stdout
using this shell trick  `2>&1`, for example
```shell
protoc --help 2>&1 | grep cpp
```

of which we shouldn't be making users have to work that hard just to
get use of --help.

+ Exhibits:
* Before:
```shell
$ protoc --help | grep cpp
Usage: protoc [OPTION] PROTO_FILES
Parse PROTO_FILES and generate output based on the options given:
  -IPATH, --proto_path=PATH   Specify the directory in which to search
for
                              imports.  May be specified multiple times;
                              directories will be searched in order.  If
not
                              given, the current working directory is
used.
  --version                   Show version info and exit.
  -h, --help                  Show this text and exit.
  --encode=MESSAGE_TYPE       Read a text-format message of the given
type
                              from standard input and write it in binary
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their
imports.
  --decode=MESSAGE_TYPE       Read a binary message of the given type
from
                              standard input and write it in text format
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their
imports.
  --decode_raw                Read an arbitrary protocol message from
                              standard input and write the raw tag/value
                              pairs in text format to standard output.
No
                              PROTO_FILES should be given when using
this
                              flag.
  -oFILE,                     Writes a FileDescriptorSet (a protocol
buffer,
    --descriptor_set_out=FILE defined in descriptor.proto) containing
all of
                              the input files to FILE.
  --include_imports           When using --descriptor_set_out, also
include
                              all dependencies of the input files in the
                              set, so that the set is self-contained.
  --include_source_info       When using --descriptor_set_out, do not
strip
                              SourceCodeInfo from the
FileDescriptorProto.
                              This results in vastly larger descriptors
that
                              include information about the original
                              location of each decl in the source file
as
                              well as surrounding comments.
  --dependency_out=FILE       Write a dependency output file in the
format
                              expected by make. This writes the
transitive
                              set of input file paths to FILE
  --error_format=FORMAT       Set the format in which to print errors.
                              FORMAT may be 'gcc' (the default) or
'msvs'
                              (Microsoft Visual Studio format).
  --print_free_field_numbers  Print the free field numbers of the
messages
                              defined in the given proto files. Groups
share
                              the same field number space with the
parent
                              message. Extension ranges are counted as
                              occupied fields numbers.

  --plugin=EXECUTABLE         Specifies a plugin executable to use.
                              Normally, protoc searches the PATH for
                              plugins, but you may specify additional
                              executables not in the path using this
flag.
                              Additionally, EXECUTABLE may be of the
form
                              NAME=PATH, in which case the given plugin
name
                              is mapped to the given executable even if
                              the executable's own name differs.
  --cpp_out=OUT_DIR           Generate C++ header and source.
  --csharp_out=OUT_DIR        Generate C# source file.
  --java_out=OUT_DIR          Generate Java source file.
  --javanano_out=OUT_DIR      Generate Java Nano source file.
  --js_out=OUT_DIR            Generate JavaScript source.
  --objc_out=OUT_DIR          Generate Objective C header and source.
  --python_out=OUT_DIR        Generate Python source file.
  --ruby_out=OUT_DIR          Generate Ruby source file.
```

* After:
```shell
$ protoc --help | grep cpp
  --plugin=EXECUTABLE         Specifies a plugin executable to use.
                              Normally, protoc searches the PATH for
                              plugins, but you may specify additional
                              executables not in the path using this
flag.
                              Additionally, EXECUTABLE may be of the
form
                              NAME=PATH, in which case the given plugin
name
                              is mapped to the given executable even if
                              the executable's own name differs.
  --cpp_out=OUT_DIR           Generate C++ header and source.
  --csharp_out=OUT_DIR        Generate C# source file.
  --java_out=OUT_DIR          Generate Java source file.
  --javanano_out=OUT_DIR      Generate Java Nano source file.
  --js_out=OUT_DIR            Generate JavaScript source.
  --objc_out=OUT_DIR          Generate Objective C header and source.
  --python_out=OUT_DIR        Generate Python source file.
  --ruby_out=OUT_DIR          Generate Ruby source file.
```

Removed a stray return statement, causing compilation error.

 optimization and quick workaround to memory leak

Merge pull request #2788 from anandolee/master

Added a header only cc_library target for the protobuf library.

Return uint32 from Log2FloorNonZero64

Add Ruby compatibilty test against 3.0.0.

Handing threading race resolving methods.

- Don't prune the extension registry as that can lead to failures when two
  threads are racing.
- If adding the method fails, check and see if it already is bound to decide
  the return result. Deals with threading races binding the methods.

A uint32 is big enough to hold any return value from that function, and
doing it this way prevents compiler warnings in coded_stream.h about
narrowing a uint64 to a uint32.

Use closurebuilder.py in favor of calcdeps.py for compiling JavaScript

Disable static analyzer for message semaphore creation

* Fix gcc 4.1.2 compilation of map_field_inl.h

Fixes "error: object missing in reference to '...'" errors from #1035

* Disable 64-bit map keys on gcc <= 4.1

* Add missing case statements

This is both more correct, and the build fails on AIX without it

This method merges the contents of the specified message into the
current message. Singular fields that are set in the specified message
overwrite the corresponding fields in the current message.  Repeated
fields are appended. Map fields key-value pairs are overritten.
Singular/Oneof sub-messages are recursively merged. All overritten
sub-messages are deep-copied.

There are two motivations for this:
1) calcdeps.py is deprecated and replaced by closurebuilder.py.
2) As part of this I was able to tweak things so that the Closure
compiler does not attempt to examine every .js file in the tree under
js/. This makes it possible to put compatibility tests and related files
in a subdirectory without them getting mixed up with the main .js files
we care about.

Removed log statement from writer_test.js

This tweak makes the test output a bit easier to read because it cuts
out a lot of unnecessary logging.

Remove the use of C++11 features.

Fix links to the license in meta-data

There might be duplicated enum values when allow_alias is true. Add PreferredAlias into OriginalNameAttribute to remove the duplication (#2727)

The first is the newer name, which is also more telling.

The "New BSD License" is the "3-Clause BSD License", but the links were
pointing to the "2-Clause BSD License".

Disable MSVC warning C4309

Fix unresolved symbols with MSVC12 and /Zc:inline

Speed up JSON parsing.

const FieldDescriptorCompare

Fix unused variables warnings in generated_message_reflection.h

README.md: Make docs URL a link

FreeBSD compatibility

Add GPBMessageDropUnknownFieldsRecursively() and tests.

GPBMessageDropUnknownFieldsRecursively() is a new helper to drop the
unknownFields from a message and all sub messages (in fields or extensions).

- Adding more detail on running tests
- Adding info about the status of .NET 3.5 support and how to enable .NET 3.5

NUnit 3.4.0 —> 3.6.0
dotnet-test-nunit 3.4.0-alpha-2 —> 3.4.0-beta-3