Added a test case to make sure future changes to ForceField do not change forces
Merged upstream changes
Made test case more tolerant of numerical differences between platforms
Merge pull request #505 from peastman/forcefield

Added a test case to make sure future changes to ForceField do not change forces
Began creating API for programmatically building and editing ForceFields
Improved API for modifying ForceField
Small fixes:
    - Adjust CharmmPsfFile parser to accept multiple blank lines before the
      NATOM record (I saw 1 PSF file like this... not sure how common it really
      is)
    - Removed the shebang line from element.py and removed execute permissions--
      it should never be executed directly (evidenced by the fact that the
      original shebang line was wrong and would never work, anyway).
    - Fix a test to determine if a Bond is part of an Angle in the PSF data
      structures.
Added start of automated conda packaging of openmm-dev.
Updated .travis.yml
Added conda recipe patch dir.
Updated preinstall script with more prereqs.
Fixed conda build.sh to build current source version, rather than online version.
Updated build.sh to change to source directory first.
Trying again with source directory.
Updated nosetests to match original .travis.yaml
Fixed binstar token; updated directory to run nosetests.
Disabled python 3.3 in build matrix because it didn't seem to be working yet.
Restore directory after Python tests.
Fixed error in after_success.sh script.
Updated encrypted binstar token.