Merge pull request #58 in CASA/casa6 from CAS-12860 to master
* commit '2ed1302d95716b73a2f14f4d7ea7465db0cb15ba':
Fix air_casawvr compilation error on osx10.15
Merge pull request #61 in CASA/casa6 from CAS-12862 to master
* commit '15f7c77eb15e4de3254f81f6f86425a22eb62818':
Added changes to fix osx error in the refantDiff test case
Merge pull request #60 in CASA/casa6 from CAS-12854 to master
* commit '13ec63a529e4fdaf3e21ffbbcfcaee5626281eba':
Updated the gainthreshold parameter description