Make cpp generated enum constants constexpr when Options::proto_h is specified

Fix copy/paste typo in CodedInputStreamTest

Fix CommonJS relative require generation, and test it

Implement IDisposable for CodedInputStream and CodedOutputStream

This fixes issue #679 and issue #1282.
(The .gitignore change is just around ncrunch; I can put it in a separate PR if you really want.)

Remove hack for building Python support with Bazel.

This change makes use of new imports attribute for Bazel's Python rules, which
enable adding directories to the PYTHONPATH. This allows us to remove
the hack for building protobuf's Python support with Bazel and now
allows projects to include protobuf using a Bazel external repository
rather than requiring it to be imported directly into the source tree as
//google/protobuf.

This change also updates the protobuf BUILD file to use a named
repository, @python//, for including Python headers rather than
//util/python. This allows projects to specify their own package for
Python headers when including protobuf with an external repository.

Fixes #1230

Fixed grpc C++ plugin support.

grpc C++ plugin generates additional files, namely .grpc.pb.cc and
.grpc.pb.h. Adding these files to the outs of the _proto_gen rule, so
dependents don't complain about undeclared inclusions. Also, compiling
the .grpc.pb.cc requires additional header files from the grpc library,
so added //external:grpc_lib to the deps of the
cc_library. Clients are expected to declare that in their bazel
WORKSPACE, pointing it to @grpc//:grpc++{_unsecure}.

Add a modified patch from craigcitro@ to handle namespace sharing.

Added grpc plugin support to cc_proto_library.

cc_proto_library now supports use_grpc_plugin flag that passes
--plugin=protoc-gen-grpc=grpc_cpp_plugin to protoc compiler
invocation. grpc_cpp_plugin is assumed to be present as
//external:grpc_cpp_plugin, so clients can setup their WORKSPACE files
appropriately to point to grpc location using bind.

Require VS2015 in the solution file

Add atomics support for 32-bit PPC.

Added support for CommonJS require()

Support ObjC Generic Collections

specified.

Validate that end-group tags match their corresponding start-group tags