Correct treatment of kappa when kappa == 0 and when there is a cutoff.
Fix misplacement of "kappa" in cutoff-GB expression.
Merge branch 'master' of http://github.com/SimTk/openmm
Merge branch 'master' of https://github.com/SimTk/openmm
Merge branch 'master' of https://github.com/swails/openmm
Merge pull request #275 from swails/master

Fixes salt concentration for GB with a cutoff