Implement NBFIX in the CHARMM parsers.
setLongRangeCorrection -> setUseLongRangeCorrection
Pass the custom force particle as a tuple of 1 parameter, rather than just as a
single parameter.
Make NBFIX ordering consistent.
Add a test for CHARMM NBFIX and import CharmmPSFWarning into the
simtk.openmm.app namespace to allow users to filter that warning out if they
want to.
Make sure the necessary files get copied over.
Make sure the parameter file gets copied over.
Merge pull request #549 from swails/charmm_nbfix

Add NBFIX support to CHARMM parsers