gst/gstinfo.*: Change gst_debug_log(_valist) to take a const format string.

gst/gstinfo.*: Change gst_debug_log(_valist) to take a const format string.

Original commit message from CVS:
2004-01-10  Benjamin Otte  <in7y118@public.uni-hamburg.de>

* gst/gstinfo.c: (gst_debug_log), (gst_debug_log_valist),
(gst_debug_message_get), (gst_debug_log_default):
* gst/gstinfo.h:
Change gst_debug_log(_valist) to take a const format string.
Change prototype of log function and functions using those to
take a GstDebugMessage instead of a string that requires using
gst_debug_message_get.