Pull request #860: CAS-14424
Merge in CASA/casa6 from CAS-14424 to master
* commit '4cfb1163eb1bbde7fdcec3ef6accde1df1611429':
substitute the viewer end-of-life URL for the placeholder string [CAS-14424]
in sdintimaging(... interactive=True, ...) post removal notice on macOS if casaviewer is not found [CAS-14424]
in deconvolve(...) post removal notice on macOS if casaviewer is not found [CAS-14424]
trap tclean(... interactive=True... ) on macOS and raise an exception if casaviewer is not available [CAS-14424]
