Fix to typo/oversight in reflection tests

This check adds a few constraints on the way to build a project when we have
a proto file which imports another one. In particular, on projects which
build both C# and Java, it's easy to end up with exceptions like

    Expected: included.proto but was src/main/protobuf/included.proto

A user may work around this issue, but it may add unnecessary constraints
on the layout of the project.

According to https://github.com/google/protobuf/commit/f3504cf3b1d456a843e8242fdee9ba0bf2991dc1#diff-ecb0b909ed572381a1c8d1994f09a948R309
it has already been considered to get rid of this check, for
similar considerations, and because it doesn't exist in the Java code

Fix #1955 clang-tidy warning misc-macro-parentheses

clang-tidy gives warning "macro argument should be enclosed in
parentheses" to macro ZR_, the "first" parameter.

fix #1342 cause by ownership issues

Make Root's +extensionRegistry generation smarter.

Fix to typo/oversight in python tests, only affecting python 3

At generation time, walk the file's dependencies to see what really contains
extensions so we can generate more minimal code that only links together the
roots that provided extensions. Gets a bunch of otherwise noop code out of
the call flow when the roots are +initialized.

Remove unused vector

Restore New*Callback into google::protobuf namespace …

update the OSGi metadata for the javanano package

Speed up ObjC Generation with large dependency trees

Don't create FileGenerators for each dep. FileGenerators will deeply create all
the message, enum, and field generators; but those aren't needed when doing
the imports for dependencies. Instead directly generate the imports off the
FileDescriptors so no extra objects are created. The only other use was when
chaining together the *Roots for the file extension registry, but that also
can be generate off the name of the FileDescriptor directly.

Ruby: make sure map parsing frames are GC-rooted.

Fixes #1966

Fix missing import of jspb.Map (#1885)

ObjC support for GenerateAll().

- Expect calls on GenerateAll() and not Generate().
- Parse the prefix validation file once, and then check all the files.

Update gmock links.

Change-Id: I3d44e3c6877e00cfea5a903568fde1e6f597aac1

The original link is no longer available.

Change-Id: I2976d3f19c8e818689549fb31ff20af8eae92a07

Add an Erlang project, gpb, to third_party.md

Fixing regular expression...

This will allow loading the extension for Ruby 2.1.10...

Move ImportWriter into helpers for sharing

Breaks the tie of the ImportWriter to the ObjC generation, allow grpc to use
a different extension and to relay the values they need for these.

- Pass in the two framework options to the ctor.
- Pass in the header extension to AddFile.

grpc likely needs to provide the same sorta handling, so expose the class so
the logic can be reused.

Add note about JSON tests maybe being wrong.

- Add note about the JSON test maybe not being correct yet.
- Add test to checks the generated names for double underscores to be sure they
  are what is expected.

More tests to shake out some cases in the json parsing

- String behaviors
- Testing only valid JSON is allowed

Adds better support for protos without packages and more warnings on possible improvements

Fixes #1844