make uniform distribution usage compatible with boost 1.46
use boost variate_generator to pass tests w/ boost 1.46 (Gaussian filler
previously filled in all NaNs for me, making many tests fail)
change all Rng's to use variate_generator for consistency
Merge pull request #49 from jeffdonahue/boosteigencompilewithboost146

make compatible with boost 1.46 and 1.55