PolConvert is implemented as a CASA task and may be installed
as described in src/INSTALL.  The machinations at this level
are needed to integrate it into a standard DiFX build process.

Prerequisits:
- define DIFXCASAPATH enviroment, which should point to the
  bin directory of your CASA installation

The installed directory contains the elements needed to use
polconvert from within CASA.  Typically you might add the
following line to your .casa/init.py file:

try:
    from os import environ
    execfile(environ['DIFXROOT'] + '/share/polconvert/mytasks.py')
except:
    print 'unable to load $DIFXROOT/share/polconvert/mytasks.py'

(or similar).  Create .casa/init.py if it does not exist.
You can then run polconvert directly from within CASA following
the sample input commands provided in (src/PP/)README.POLCONVERT
which should be installed in DIFX_ROOT/share/polconvert.