Made ordering of improper torsions more consistent.  Also fixed a bug related to Drude particles.
Fixed an error in the computation of Drude screening force
Created option so virtual sites can share the exclusions of their parent
Changed definition of polarizability to match CHARMM
Created XML file for CHARMM polarizable force field
Added CHARMM polarizable force field to the list of force fields in the manual
Fixed some incorrect test cases.
Trivial change to force travis to rerun the tests
Merge remote-tracking branch 'origin/master' into charmm
Depressing compromise to make the ordering of atoms in improper torsions as consistent as possible with both AMBER and CHARMM
Merge pull request #531 from peastman/charmm

Implemented CHARMM polarizable force field