Pull request #947: CAS-14432
Merge in CASA/casa6 from CAS-14432 to release/6.6.6
* commit '903bfec8f37ebb5269b3395a8b7530dd2941a0b2':
For CAS-14432, removed accidental <CR> from last commit; added missing (python) close of igs file
For CAS-14432, fixed exception-handling for no-internet case; added better error messages for retrieval failures
For CAS-14314, fixed log message typo.
For CAS-13742, tidy up exception handling around TEC file retrieval; ensure retrieved file lands in cwd, even if user has changed it, and removed latex-y \mathrm junk from plot label formation since they don't work anymore, and aren't even necessary.
For CAS-14432, force antpos caltable creation for data from online tropo delay model error, even when there are no antpos corrections required.
