gst/gstinfo.c: Add mutex to serialise access to the hash table with the function pointer => function name string mapp...

Original commit message from CVS:
Reviewed by: Tim-Philipp Müller  <tim at centricular dot net>
* gst/gstinfo.c: (_gst_debug_nameof_funcptr),
(_gst_debug_register_funcptr):
Add mutex to serialise access to the hash table with
the function pointer => function name string mapping;
make that hash table static scope (#316809).
* gst/registries/.cvsignore:
Remove left-over file.