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
Updated long range correction code to work with new style tabulated functions
Merge pull request #529 from peastman/master

Updated long range correction code to work with new style tabulated functions
Changed definition of polarizability to match CHARMM
Created XML file for CHARMM polarizable force field
Change the default so that NBFIX amber topology files use a long-range
correction by default. Then add a test for using the long-range correction and
_not_ using the long-range correction.  Comment out the test using the
long-range correction since it currently segfaults.  When the fix for the
segfault is added, this test can be reinstated (but the energy has to be
updated)

This change in default makes it consistent with the default behavior for the
classical NonbondedForce, and I would have set that as the default to begin with
if I had known it was supposed to work.
Update the energy in anticipation of just uncommenting that test when the fix is
added.
Added CHARMM polarizable force field to the list of force fields in the manual
Merge pull request #530 from swails/longrange

Update default long-range option and expand test
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
Revert to older Travis-CI testing framework so we can separate testing from conda dev builds.
Merge pull request #533 from jchodera/revert-travis-ci

Revert to older Travis-CI testing framework to separate testing from conda dev builds
Fixed bug when running on a CPU device
Merge pull request #535 from peastman/master

Fixed bug when running on a CPU device