Merge pull request #502 in CASA/casa6 from CAS-13618 to master
* commit '65556d9556d9bf5762217233723ac766d377f1ce': CAS-13618 : Edited new tests to leave out known unsupported modes.
pushed the wrong changes in the last commit ...this is what was intended
tst3 and ts4 in mixed_cube_IQUV did not have enough degrees of freedom to clean UV images...So added a box mask to the tclean command.
Updated Cube tests. ( Added stk-requested doc edit in xml - unrelated)
Added (and skipped) cube tests for I,U, IQUV CAS-13618 : Edit to the test script (after figuring out how to run it locally to debug it) CAS-13618 : Enabled full pol tests. Now, it has Stokes I, Stokes U, and Stokes IQUV imaging tests.
Making sure sumwt respects real sumweight of each pol used rather than just the first CAS-13618 : Added the task imports needed for casa6 runs of the test script... CAS-13618 : Added verification tests
cleaned up the code a bit
do a check of polmap at every vb if necessary
CAS-13618 : Edited new tests to leave out known unsupported modes.
( Also edited XML inline docs for the pblimit parameter to help close out an unrelated ticket CAS-9371 that was pending just this doc edit)
