Merge pull request #1373 from casacore/1372-msfitsoutput-needs-small-fix-to-convert-proper-motion-units
correct proper motion unit conversion in MSFitsOutput.cc
Modified previous change to use Quanta
Now making use of the Quanta features to achieve conversion of the proper motion values to deg/day.
In case this fails (exception), fall back to old behaviour and write values without conversion but issue Warning.
correct proper motion unit conversion in MSFitsOutput.cc
Check the present units and if they are RAD/S, convert to
DEG/DAY, otherwise write the values as they are and give warning if the original units were not DEG/DAY.