* Give a unique category to each test.

This change introduce a TestCategory enum to ConformanceRequest. Existing tests
are divided into three categories: binary format test, json format test and json
format (ignore unknown when parsing) test. For the previous two categories, there
is no change to existing testee programs. For tests with the last category, testee programs
should either enable ignoring unknown field during json parsing or skip the test.

* Fix python test

* Fix java

* Fix csharp

* Update document

* Update csharp generated code

* Factored Conformance test messages into shared test schema.

* Updated benchmarks to use new proto3 message locations.

* Fixed include path.

* Conformance: fixed include of Python test messages.

* Make maven in Rakefile use --batch-mode.

* Revert changes to benchmarks.

On second thought I think a separate schema for
CPU benchmarking makes sense.

* Try regenerating C# protos for new test protos.

* Removed benchmark messages from test proto.

* Added Jon Skeet's fixes for C#.

* Removed duplicate/old test messages C# file.

* C# fixes for test schema move.

* Fixed C# to use the correct TestAllTypes message.

* Fixes for Objective C test schema move.

* Added missing EXTRA_DIST file.