Adding function prototypes with this patch.

This helps ctypes know the calling conventions it should use to communicate
with the binary interface of libgfapi and which types it should allocate and
cast. Without it, ctypes fails/crashes when not running on the main thread.

Change-Id: I73480229f451167377ed4d1534b08b66c689cc4f
Signed-off-by: Humble Chirammal <hchiramm@redhat.com>