Refactor Travis tests: split configs and run in parallel.

Merge protobuf C# into master (only C# proto2 is supported)

ruby: make repeated_field quack like an array

Add Ruby to Travis testing

Integrate changes from latest master branch into csharp branch.

- Added RVM-based Ruby test driver that tests MRI and JRuby.
- Fixed JRuby compilation (at least in my current setup): force source
  version to 1.6 (Java 6) to allow generics and annotations.
- Modify the skipped JRuby JSON tests so that the exit code is 0 (skip()
  results in a failing exit code from `rake test`). An upcoming PR
  should fix JSON under JRuby in general soon.

Update README.md for C#

Remove the C#-specific field_presence_test.proto, using unittest_no_field_presence.proto instead.

This is the start of establishing a C# namespace of "Google.ProtocolBuffers.TestProtos.Proto3" for proto3-syntax protos.
We could optionally split the directory structure as well into Proto2 and Proto3 for clarity.

C# generate_proto.sh and buildall.sh scripts

C# cleanup

Dockerfile for building protoc on Centos 6.6

Fixes for Mono

Uncomment conflict fields from pkg-config files.

Convert back to using NUnit, which is now loaded via NuGet.

The referenced bug was fixed in 2007 and has been released in pkg-config-0.23
(16.Jan.2008). The fixed version is widely available.

This includes the NUnit test adapter which allows NUnit tests to be run under VS without any extra plugins.
Unfortunate the compatibility tests using the abstract test fixture class show up as "external" tests, and aren't well presented - but they do run.

Change-Id: I23dee1c1d27b6440658680e9c273b6250213123c