Fix binding for NULL
getOption[A] for NULL values

- get[A] doesn't support NULLs (and probably shouldn't).
- Make None usage symmetrical.
Support finagle connection pooling

This patch leaves the Client able to be used with a user-provided
ServiceFactory, for configurable hostConnectionLimit, timeouts,
logging, etc.

* Fix Client.close() to close its underlying service rather than the
  service factory (which was a noop).

* Add Client.resetConnection(), which can be used to reset a
  connection back to a state before any statements were prepared.

* Add support for "DISCARD ALL" to Connection and Messages in support
  of resetConnection().

* Move the authentication proxy and errors proxy to prepareConnFactory
  (from prepareServiceFactory) so they're connection-scoped rather
  than factory-scoped.
Merge pull request #27 from thefactory/upstream-connection-pooling

Support finagle connection pooling
Merge pull request #25 from thefactory/fix-bind-null

Fix binding for NULL
Refactor get[A] to use getOption[A]
Merge branch 'row-get-option' of github.com:thefactory/finagle-postgres into thefactory-row-get-option
Code cleanup
Support UPDATE..FROM..RETURNING statements

These work like SELECTs but allow you to update fields before
selecting the data.
Merge pull request #28 from pteichman/update-from-returning

Support UPDATE..FROM..RETURNING statements