Added missing serialization support for CustomNonbondedForce interaction groups.
Undid some debug info.
Undid an erroneous commit.
Undid more erroneous changes.
Rolled back one more change.
Added missing serialization for some other properties of CustomNonbondedForce.
Updated tests of serialization of CustomNonbondedForce, though test omits comparison of interaction group sets since I couldn't figure out how to do that.
Added serialization of more properties, as well as unit test extensions for these additions.
Added assertion utility to compare containers.
getBoolProperty() now returns bool, instead of it.
Changed tabs to spaces.
Removed code left over from debugging.
Fixed same issue in NonbondedForce serialization.
Added missing serialization of PME parameters alpha, nx, ny, nz for NonbondedForce.
Added defaults to make serialization of CustomNonbondedForce and NonbondedForce backward-compatible.
Removed fiels that didn't below.
Undo changes.
Added defaults for backward compatibility.
Fixed a bug in serialization.
Merge pull request #410 from jchodera/debugging-group-interactions

Added missing serialization support for CustomNonbondedForce group interactions