Pull request #943: CAS-14589: CLONE of CAS-14575 for 6.7.1 (mstransform history)
Merge in CASA/casa6 from CAS-14589 to release/6.7.1
* commit 'c725ccbd1303359309974baee6ff7bccadaf5b1c':
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