Pull request #755: CAS-11876
Merge in CASA/casa6 from CAS-11876 to master
* commit 'b1e892e5908a745896a8ca0f7d586b5d49693b64':
Minor edit
move mslisthelper to a new location
A minor edit - remove a commented line
Added sorting of the data sel parameters when vislist is sorted by time
Set testcontent=False in check_mslist in order to identify missing SPECTRAL_WINDOW column properly. Also added sorting vis list with time.
Updated checkall argument to use with the casatestutils' imagerhelpers
Incorporated check_mslist function to check conformance of the list of MSs into the code
Use the new function, check_mslist in tclean as well as fixes for concat and virtualconcat tasks
Added a variant for CAS-11876 test for CAS-11833
Fixed a bug
Removed debugging statements, fixed the check weight spec Python function, and added a logger message when modifying an MS to add the weight spectrum
Added workaround and debug statements
