Merge in CASA/casa6 from CAS-13877 to master
* commit '6e66f2f57fdc101f0e9220e90784cb72ad05187b':
remove cruft [CAS-13877]
Update PlotMS version to 1.8.7
Update build.conf
Update PlotMS reference to 1.7.3a13877.dev3
xml-casa fetch jar file if it doesn't exist (allowing use from source tree) [CAS-13877]