LDAResults.predict speedup and cmd module rename

cleaned up changes to vw_helpers.py to hide tokenset per Ian's comments 

sped up LDAResults.predict by ~5x.  Renamed 'cmd' module to 'cmdutils' to avoid conflict with native python 'cmd'.  I don't know how you guys feel about pull requests, but I think these changes would be useful for others.  Thanks for letting me use your code.  -Louis