* Fix php well known type conformance tests
* Properly generate code for test.proto
* Provide GPBMetadata files in c extensions for generated files to import.
* Remove unnecessary test
* Clean up code
* Add declaration for initOnce.
* Refactoring
* Fix php well known type conformance tests
* Properly generate code for test.proto
* Provide GPBMetadata files in c extensions for generated files to import.
* Remove unnecessary test
* Clean up code
* Add declaration for initOnce.
* Refactoring
* Reserve unknown in ruby
* Revert ruby tests. Wait for cpp impl for conformance test
* Add conformance test for preserving unknown
* Add unknown field conformance test to csharp failure list.
* Fix comments
* Fix comment
* Fix comments
* Fix typo
* Use stringsink_string directly
* Mark hd unused
* Remove unused encodeunknown_handlerfunc
This better shows the semantic of the API. For already setted fields,
mergeFromString do replacement for singular fields and appending for
repeated fields.