Added CLI option internal_access for types (C#)

Do not link in pthread library for Android builds.

* `csharp_options`: Added `Options` to encapsulate generator options.
   Supported options for now - file_extension, base_namespace
* `{Blah}Generator`: Now accept `Options*` as parameter to constructor
* `csharp_generator.cc`: Parse and populate options
* `Makefile.am`: Added `csharp_options.h`
* `extract_includes.bat.in`: Added `csharp_options.h`

Refactoring code to two commits. This is the first commit

This is required to allow Tensorflow to build on Android without hacks. Currently we create a dummy pthread library just to satisfy this dependency for a library that does not exist on Android. See https://github.com/google/protobuf/issues/1373 for more context.

Added deprecated option handling to objective-c

Linking the cpp implementation extension statically with libprotobuf

Remove duplicate test cases.

Add -position and -isAtEnd for use when manually parsing input streams.

(NCrunch noticed these.)

Introduce a new nuget package, Google.Protobuf.Tools, basically to contain protoc on multiple platforms.

Added an API to allow oversize protos when using C++ extension in Python

Replace #include <iostream> with #include <ostream> in int128.cc

Introduce a new nuget package, Google.Protobuf.Tools, basically to contain protoc on multiple platforms.

I've moved both protoc.exe and the proto files out of Google.Protobuf.
The .proto files aren't a slam-dunk, but it feels like they belong with protoc as you'd *use* them with protoc.
It's not clear to me whether we really need both an x86 and x64 version of protoc.exe, as x86 would work on 64-bit Windows anyway. Discuss :)

Refactoring of FieldDescriptor

iostream is not actually necessary here, and it introduces unnecessary
static initializers.

Use the T() instead of NULL for the default value.

Add support for running on Jenkins

This makes no externally visible behavioral changes. Internally and non-behaviorally:

- We use a field (compiler-generated) to store the JsonName to avoid recomputing it repeatedly
- The documentation for JsonName is updated to reflect the meaning better
- Readonly autoprops and expression-bodied properties used where possible

csharp: add support for the json_name option

The template can be specialized on primitives, e.g. double, where
converting NULL will trigger a warning.

Mark iOS tests as able to fail.

Travis updated their images to include an xctool that can randomly kill
tests, so mark them as flaky to avoid turning things red.

The message was autoreleased, the -releases are an over release.

export well known protos

Update coded_stream.h

fix warning treated as error prevents building on 64-bit windows.

Allow custom URLs for Any in JsonFormat

Only create the readonlySemaphore on demand.

This will lower the amount of dispatch_semaphores created per Message when the
full object tree isn't walked in a way that would require them to be created.
Uses a dispatch_once_t for one time init of the dispatch_semaphore.