Check for energy-dependent multiplicity in ACE file.
Merge pull request #296 from paulromano/multiplicity

Check for energy-dependent multiplicity in ACE file

All tests pass; merging and closing.
Fix distance-to-surface calculationg for general plane surface.
account for differences in band probabilities at different energies
Change quick install instructions to be more explicit about checking out branch
master.
updated test results
Have update_results.py run OpenMC twice when generating results for
test_source_file. Closes #288 on github.
Merge remote-tracking branch 'mit-crpg/openmc/develop' into band-samp
update source file test reference results
Merge pull request #299 from paulromano/plane-distance-fix

Fix distance-to-surface calculation for general plane surface
threadsafe particle restart writing
Merge pull request #300 from walshjon/band-samp

account for differences in band probabilities at different energies
Allow zero atom/weight percents in materials. Closes #301 on github.
Don't use PWD environment variable when setting path to input files. Closes #302
on github.