gst/gstpreset.c: Use g_unlink instead of unlink.

gst/gstpreset.c: Use g_unlink instead of unlink.

Original commit message from CVS:
* gst/gstpreset.c:
Use g_unlink instead of unlink.
* gst/gststructure.c:
Use glib type.
* gst/gstutils.c:
Add a FIXME:.
* gst/gsttaglist.c:
* gst/gsttypefind.c:
* gst/gstvalue.c:
Formatting & whitespaces.