Get rid of the Random context and add the support directly to python.

Get rid of the Random context and add the support directly to python.
We don't currently use randomness much, so I didn't go too far, but
in the future, we may want to actually expose the random number values
themselves to python.  For now, I'll at least let you seed it.
While we're at it, clean up a clearly bad way for generating random
doubles.

--HG--
extra : convert_revision : df2aa8b58dd0d9c2a7c771668a760b2df8db1e11