There was some nasty global-ish variable reference updating happening when the native module 'initializes' after its require with `require('pg').native`
This fixes the issue by making sure both `require('pg')` and `require('pg').native` each initialize their own context in isolation and no weird global-ish references are used & subsequently stomped on.
Adds a check in the error listener on the client in the pool, to
prevent calling destroy on a client when it is already being
destroyed.
Without this check, if an error occurs during the ending of the
stream, such as a timeout, the client is never removed from
the pool and weird things happen.
