Improvements to Connection auto-invalidation

Improvements to Connection auto-invalidation
handling.  If a non-disconnect error occurs,
but leads to a delayed disconnect error within error
handling (happens with MySQL), the disconnect condition
is detected.  The Connection can now also be closed
when in an invalid state, meaning it will raise "closed"
on next usage, and additionally the "close with result"
feature will work even if the autorollback in an error
handling routine fails and regardless of whether the
condition is a disconnect or not.
[ticket:2695]