Allow VW() instances to connect to existing VW daemons

[mokelly]

Addresses #3:

--VW() can connect to existing VW daemons
--daemon_mode can be used to launch a daemon VW instance and connect automatically

[ztane]

Btw, given ip 10.12.34.56 and port 666, one gets:

File "wabbit_wappa/active_learner.py", line 74, in __init__
    raise
RuntimeError: No active exception to reraise

That is, raise is valid in except block only

[ztane]

Ah, also, in any prod setting, if connection to existing daemon fails, I want to get the exception instantaneously and not 5 seconds later ;)

[ztane]

thus at least

    while True:
        ...
        except socket.error:
            connection_tries += 1
            if connection_tries >= MAX_CONNECTION_TRIES:
                raise socket.error

            time.sleep(CONNECTION_WAIT)