gst/gstobject.c: Random micro-optimisation: don't use a hash table with strings as keys and the usual strdup/strcmp i...

Original commit message from CVS:
* gst/gstobject.c: (gst_object_set_name_default),
(gst_object_set_name):
Random micro-optimisation: don't use a hash table
with strings as keys and the usual strdup/strcmp
involved, but rather just use the GQuark of the
type name as key, since it needs to be looked up
anyway to get the type name string.
* tests/check/gst/gstobject.c: (GST_START_TEST):
Fix various leaks.