Revision 665548

[thrift] PHP thrift_protocol extension, revision 2.0

Summary:
  All PHP serialization and deserialization can now happen in extension-land,
  which should be much faster. This includes reading message headers and all
  complex types (structs, exceptions, whatever).

  The compiler has been updated to always emit the $_TSPEC static array for
  generated PHP code, since the new extension depends on it.

  As before, the PHP code gates enabling the accelerated serialization on
  the protocol being an instance of TBinaryProtocolAcclerated and the function
  for the [de]serialization operation existing.

  The function names have changed since the last version of the extension,
  so old and new generated code can coexist, and new generated code can run on
  a server with the old extension (but it will not use accelerated serialization).

Reviewed by: hzhao
Test Plan: Generated a couple of endpoints and called their services through the
  new extension. Both use a variety of nested complex types. Built and ran the
  extension in php-5.2.3 in debug mode, killed the reported memory leaks.