Pull request #758: CAS-14200
Merge in CASA/casa6 from CAS-14200 to master
* commit '6e7c75489cf6ca6c024449cbfcb25bc771537478':
switched to date conversion using quanta tool
updated test case for ant pos time limit
Added a conversion for the dates into counts for days. This is a rough assumption i.e. years being 365 days months being 30
Added mechanical test for new ant_pos_time_limit parameter
fixed subparameter setting in xml
was accidentally applying offsets twice causing test failures
fixed param default
Added new param to gencal called ant_pos_time_limit. This will set a time limit in days after which corrections are not included in the final offset. Bryan's code was added to the existing evla antenna posn correction script
