gst/mxf/mxfdemux.c: If the preface references a primary package use this as the defau...

gst/mxf/mxfdemux.c: If the preface references a primary package use this as the default playback package unless one w...

Original commit message from CVS:
* gst/mxf/mxfdemux.c: (gst_mxf_demux_choose_package):
If the preface references a primary package use this as the default
playback package unless one was specified by the "package" property.
If there's no preface primary package still try to use the first
material package.