Improve unit handling in charmm crd file classes.
Merge pull request #477 from swails/fix_charmm_crdunits

Improve unit handling in charmm crd file classes.
Add virtual sites
Out of plane
Merge pull request #478 from mpharrigan/vs

Add virtual sites
Merge branch 'master' of https://github.com/SimTk/openmm into exclusions
Reverted a change that is no longer necessary