Resolved issue in likelihood calculation for LDA.  Note that likelihood calculation is relatively slow (costly) and probably should not be enabled by default.
To accelerate likelihood calculations I have added code to precompute the loggamma for a range of common values.
Merge branch 'master' of https://github.com/graphlab-code/graphlab
Merge pull request #44 from jegonzal/lda_likelihood_calculation

Improved Likelihood calculation stability.