ext/libmms/gstmms.c: Return FLOW_UNEXPECTED on EOS, not FLOW_ERROR. Also, no need to push our own EOS event on EOS, t...

Original commit message from CVS:
* ext/libmms/gstmms.c: (gst_mms_class_init), (gst_mms_create),
(gst_mms_start):
Return FLOW_UNEXPECTED on EOS, not FLOW_ERROR. Also, no need to
push our own EOS event on EOS, the base class will do that for us;
fix bogus query code; post semi-decent errors on the bus when an
error occurs in ::start(), otherwise the user will get to see
whatever cryptic default message GstBaseSrc comes up with.