Seem to have fixed the L(I) issue, testing now
Fixed an issue where if ACE files first angular distribution for a given incoming energy was isotropic (LC=0), then the length calculation would be incorrect since rxn%adist%location(1) was 0.
Fixed sample_angles interpolation of mu.  The old way was resulting in mus outside the range of [-1,1] and was effectively using the slope of the randomly selected bin but extrapolating to the next lower bin.
Info in Troubleshooting portion of manual regarding L(I) issue is no longer needed. Removed.
Corrected ace reading to look for the existence of the same locator anywhere in the array instead of just after, and updated the tests.
Fix bug in source file test.

When looking for a source file, it was assumed that the current working
directory did not contain the character '.'. If the working directory did
contain a '.', this test would fail.
Merge remote-tracking branch 'upstream/develop' into lc_fix
Merge branch 'lc_fix' of github.com:nelsonag/openmc into lc_fix
Updated results_true.dat to  correspond with the updated test.
Add try/finally in tests to make sure teardown() is called.
Merge remote-tracking branch 'upstream/develop' into lc_fix
Merge pull request #278 from nelsonag/lc_fix

Fixes to support reading of older cross-section data sets
Merge branch 'develop' into ndpp_harmonic