Support mixedpol calibration in post-processing

[iniyannatarajan]

Stages 7 and 8 should indicate to the calibration routines if the input UVFITS files are in polconverted or mixedpol format.

[iniyannatarajan]

Added a MIXEDPOL environment variable to the 0.launch script for the post-processing stages (4bb3e67, 9257030). Setting MIXEDPOL to true using either SET_MIXEDPOL=true or the -m option switches the mixedpol mode on when calling the EAT executable applycal.