Add the client host IP address and port to application_name.

This is enabled by a config parameter which defaults to 'on'

If the client subsequently overwrites the application_name parameter
during the session then this won't be sticky, but it does let you see
(and log) where queries are actually coming from instead of just seeing
pgbouncer as the source address and port.
Merge pull request #23 from pgexperts/appname-hostport

Add the client host IP address and port to application_name.