Update version number to 3.0.0-alpha-3

Undef GOOGLE_PROTOBUF_MISSING_HASH after it is used.

Objective C Second Alpha Drop

- Style fixups in the code.
- map<> serialization fixes and more tests.
- Autocreation of map<> fields (to match repeated fields).
- @@protoc_insertion_point(global_scope|imports).
- Fixup proto2 syntax extension support.
- Move all startup code to +initialize so it happen on class usage and not app startup.
- Have generated headers use forward declarations and move imports into generated code, reduces what is need at compile time to speed up compiled and avoid pointless rippling of rebuilds.

down-integrate internal changes

Add default import paths for descriptor.proto and well-known protos.

Include well-known types in Java runtime.

Change-Id: I816fe2fac7fccbcd96dd8510c7c9b5e7996aeadc

Change-Id: I4afa295de4c8ed2a4cd0919cf84aedcd1327d9a5

Adds a podspec for the proto3 Objective-C runtime.

Getting the ObjC generator building on Windows.

Solves AOT compilation issue for Unity - iOS

added concrete IEqualityComparer<ExtensionIntPair> implementation in ExtensionRegistryLite.cs to prevent AOT compilation issue with unity in iOS

Marked compiler literal unsigned.

C# travis integration

When compiling a protobuf with gcc 3.3.2 for powerpc, I ran into the
following warning message:

INFO: From Compiling my_proto.pb.cc powerpc-603e-linux-gcc:
bazel-out/local_linux-dbg/genfiles/my_proto.pb.cc: In member
   function `virtual void MyProto::Clear()':
   bazel-out/local_linux-dbg/genfiles/my_proto.pb.cc:223: warning: this
      decimal constant is unsigned only in ISO C90

The line in the proto file that was triggering it was:

  if (_has_bits_[24 / 32] & 4278190080) {
    ZR_(field1_, field2_);
  }

_has_bits_ is a uint32.  The constant mask should therefore be
unsigned.  This change updates the constant to be generated as
unsigned.

Remove the ClassList support (maybe bring it back in the future).
Trim the includes to hopefully get a working Window build.
Add some more returns after switches for compilers that warn even when all values of the enum are handled.
Use ghtonl instead of htonl.
Change the use of [u]int(8,32)_t within the ObjC generator code to [u]int(8,32) to match the rest of the compiler.
Add objective-c generator files to Visual Studio project.

Ruby C extension speedup: don't re-intern constant string needlessly.

Also fixed lines with > 80 char length.

Generate *all* protos in the script, applying fixups.

Update MRI C Ruby extension to use new version of upb (with upb_env).

Post csharp landing fixup.

Re-add the objc prefix that got removed by accident.
Regenerate the generated descriptors (C++ and ObjC).

We still have some protos which aren't generated how we want them to be:

- Until we have an option to specify the "umbrella" class, DescriptorProtoFile
  will be broken. (The change of name here affects the reflection descriptor,
  which accounts for most of the change. That's easier than trying to work out
  exactly which occurrences of Descriptor need changing though.)
- That change affects UnittestCustomOptions
- Issue #307 breaks Unittest.cs

After this commit, we don't have the record of the fixups in the files themselves
any more, but one centralized record in the shell script.

[PYTHON] Only generate protos in development

Fixes #333.

- Alter encode/decode paths to use the `upb_env` (environment)
  abstraction.
- Update upb amalgamation to upstream `93791bfe`.
- Fix a compilation warning (void*->char* cast).
- Modify build flags so that upb doesn't produce warnings -- the Travis
  build logs were pretty cluttered previously.

ruby: Encode decode cleanup and behavior normalization