improve mxfRational equality operators
improve mxfRational equality operators

Account for 2500/100 == 25/1 case for example, i.e. don't simply
compare the numerators and denominators.

stuarthicks/libmxfpp,Limecraft/ebu-libmxfpp,stuarthicks/libmxfpp,Limecraft/ebu-libmxfpp,Limecraft/ebu-libmxfpp,stuarthicks/libmxfpp