Pull request #1043: CAS-14606
Merge in CASA/casa6 from CAS-14606 to master
* commit 'e2af0ec57f50d3edffed7dd5384465472326b4a5':
Add a check that an entire (sub-)table is empty (nrows=0)
Fix a bug in is_column_empty function and add tb.getvarcol-based data existence check for the subtables
Add test for data types, str, int, float
Access the first row only
Use tb.getvarcol to check if optional data columns in Main table have any data instead of tb.getcell
