Add sanity test system to OSS benchmarker

Summary: Check that we're getting an expected substring in the response.

Reviewed By: @JoelMarcey

Differential Revision: D1536933
Fix double deallocation of object in zend conversion of object to string

Summary: fixes #2844

runtime/ext_zend_compat/hhvm/zend-wrap-func.cpp line 80 - 102 deallocates the object twice.
The first time is when the object is parsed as a string, and the second time is in
frame_free_local_inl.

parse_arg_object_to_string is only called from one place, so I don't think it will have
side effects on other code.

Reviewed By: @ptarjan

Differential Revision: D1526334