With 'extern "C"' issue with PHP5 compat layer

Summary: "fopen_wrappers.h" was #include'ing files inside an 'extern "C"' block,
which caused problems when trying to use C++ features in certain C++ header
files such as "name-value-table-wrapper.h".

This diff fixes "fopen_wrappers.h" so that it doesn't #include files inside
an 'extern "C"' block.

Reviewed By: @edwinsmith

Differential Revision: D1648885

Signature: t1:1648885:1414659015:03793b6f9b204293375d314e44b2eac3dc1fff77