#92 MPEGVideoDescriptor r-tags currently set to dummy values

[Jesse Low]

In the AAFMetaDict.xls spreadsheet the r-tag values for
MPEGVideoDescriptor are currently set to actual values
for testing purposes. They should be set to zero
because the PIDs for MPEGVideoDescriptor are
dynamically generated but the infrastructure required
for this is not yet in place, so to allow the test
programs to run properly fake values have been set.
When the dynamic pid code is in place, these fake
values should be set back to zero.