ext/divx/gstdivxenc.c: Use explicit caps - fix capsnego.

ext/divx/gstdivxenc.c: Use explicit caps - fix capsnego.

Original commit message from CVS:
2004-01-09  Ronald Bultje  <rbultje@ronald.bitfreak.net>

* ext/divx/gstdivxenc.c: (gst_divxenc_init):
Use explicit caps - fix capsnego.
* ext/xvid/gstxviddec.c:
* ext/xvid/gstxvidenc.c:
Remove macro-inside-macro which caused compile errors.
* gst-libs/gst/riff/riff-read.c: (gst_riff_read_header):
Error out if it's not a RIFF file. Else we error out without
gst_element_error() which is not good...