Added PasswordAuthenticator and associated code.

Added password auth code.

Upped the upper bound on base to work with 7.8.2. Changed tests to use
Auth. (Default not using auth)

The auth data was added to Pool as it's being used by the ReaderT and seems ok to me. 

I had issues with the tests returning Invalid on dropping non existent tables, so I tweaked the tests.

Sorry about the unnecessarily modified lines. I have Emacs killing whitespace at end of lines.

Tested against Cassandra 2.0.9