Fastcgi execution file implementation fixes

Make the fastcgi implementation more robust in detecting the
filename to execute.
Support for files outside of document root.
Removed Duplicate CopyPathInfo so it only does this once.

Closes #1702
Closes #1708

Reviewed By: @scannell

Differential Revision: D1159825

Pulled By: @ptarjan

Conflicts:
	hphp/runtime/server/fastcgi/fastcgi-transport.cpp