gst/gstformat.c: Fix locking order (must take lock before using n_values).

gst/gstformat.c: Fix locking order (must take lock before using n_values).

Original commit message from CVS:
* gst/gstformat.c: (gst_format_register):
Fix locking order (must take lock before using n_values).
* gst/gstvalue.c: (gst_value_serialize_enum),
(gst_value_deserialize_enum_iter_cmp),
(gst_value_deserialize_enum):
Fix serialisation/deserialisation of custom registered GstFormats.
* tests/check/gst/gstvalue.c: (GST_START_TEST), (gst_value_suite):
Unit test for custom format serialisation/deserialisation.