- Fixed critical issue whereby the pool "checkout" event handler

- Fixed critical issue whereby the pool "checkout" event handler
may be called against a stale connection without the "connect"
event handler having been called, in the case where the pool
attempted to reconnect after being invalidated and failed; the stale
connection would remain present and would be used on a subsequent
attempt.  This issue has a greater impact in the 1.0 series subsequent
to 1.0.2, as it also delivers a blanked-out ``.info`` dictionary to
the event handler; prior to 1.0.2 the ``.info`` dictionary is still
the previous one.
fixes #3497

(cherry picked from commit 4096ad0f0980f6940be57aaee85791df8f975cd7)