Merge Google internal changes

Fix cp -r usage to be portable.

cp -r foo/ bar/ in linux will create a bar/foo directoy. In the
objectivec generate descritpor case, well known types will be created in
objectivec/google/google/protobuf/.. if the command is run under linux.

Adding the trailing period fixes the behavior inconsistency.

Added dig and bsearch_index to RepeatedField methods forwarded to array

Fix up -hash/-isEqual: for bool storage.

Both methods weren't checking the has_bits (where the bools are stored), so
it resulted in invalid results.

Add a test that should shake out something like this in the future also.

This fixes the test_acts_likes_an_array test in RepeatedFieldTest, which
checks that repeated fields respond to the same methods as regular Ruby
arrays. The bsearch_index and dig array methods seem to be new in Ruby
2.3 and so we should support those.

Updated upb and simplified ruby code a bit with new upb method.

Proper checking of enum with non zero default

proto2 syntax allows the first enum to have a non zero value. This means any
field using that default has a non zero default without having an explicit
default being set. So when deciding what runtime info is needed, don't rely
on an explicit default, always check that the values aren't zero.

Fixes https://github.com/google/protobuf/issues/1453

Added serialVersionUID to ExtendableMessage.

* Add initial design doc for Swift protocol buffers.

Add a docs directory and move the third-party add-ons page here.

Change protobuf CPP proto generator to support the 'lite' option in

Remove googletest.h header from stringprintf.cc

Regenerate descriptor/well-known types for C#

(There are documentation changes and new fields in descriptor.proto that have resulted
in changes to the serialized descriptor, but no breaking changes for C#.)

ObjC support for failing the build in the generated WKTs are out of date

- Always generated into a temp directory so we can see if things changed.
- Add a flag to control exiting with error when stale vs updating.

This should let the continuous builds error out when ObjC needs to have the
checked in sources updated.

Enum casing in C#

Support Windows in gulpfile.js

(JSON parsing already does the right thing.)

JSON tests fail, as we're not using OriginalNameAttribute yet.

Overview of changes:
- A new C#-specific command-line option, legacy_enum_values to revert to the old behavior
- When legacy_enum_values isn't specified, we strip the enum name as a prefix, and PascalCase the value name
- A new attribute within the C# code so that we can always tell the original in-proto name

Regenerating the C# code with legacy_enum_values leads to code which still compiles and works - but
there's more still to do.

Add missing includes in field mask test

Fix comments typo and update WKTs

Add missing PY2AND3 srcs_versions attributes to Python Bazel build targets

Update file list to include the missing extension lite file.