Pull request #942: CAS-14588: CLONE of CAS-14575 for 6.6.6 (mstransform history)
Merge in CASA/casa6 from CAS-14588 to release/6.6.6
* commit 'a9d00f53061f78dfc902734c719196e9240a20ef':
add some checks on history writing in test_mstransform, CAS-14575
do write warning msg if problems with the ms instance in write_history, CAS-14575
avoid assigning None to mslocal while still needed, CAS-14575