Updated .travis.yml to try to get it to build.
Now use conda for installation of openmm, and clone repex from github.
Removed duplicate installation of mdtraj.
Tried to fix conda install of openmm.
Removed matplotlib conda install from .travis.yml because it was failing:
Error: MD5 sums mismatch for download: matplotlib-1.3.1-np18py27_0.tar.bz2 (77afd2ec93406bfc41a0b2d686f5d59f != d34da390d0339ef9cd23c66dd3fd3597)
Fixed pymbar version spec in .travis.yml
Fixed stall at checkout of repex.
Removed some tests from tests/test_alchemy.py nose tests because they were too slow for travis-ci CPU platform.
Merge pull request #32 from jchodera/master

Fixed travis-ci, though not all doctests are working yet.  nosetests for tests/test_alchemy.py work.