only a warning and linking would fail later on. Not much sense in making jpeg
support conditional. What use is a mjpeg package without jpeg support? ;)
Also, remove checks for the jpeg-mmx package. That either 1) does not
work (crashes) or 2) will not build at all on many platforms. Also remove
jpeg-mmx from the spec file so that RPMs do not give the impression that
the jpeg-mmx is usable.
