the URL design a little simpler

:meth:`.Connection.invalidate` method, or an invalidation due
to a database disconnect, would fail if the
``isolation_level`` parameter had been used with
:meth:`.Connection.execution_options`; the "finalizer" that resets
the isolation level would be called on the no longer opened connection.
fixes #3302

_handle_dbapi_exception_noconnection() to only invoke in the case
of raw_connection() in the constructor of Connection.   in all other
cases the Connection proceeds with _handle_dbapi_exception() including
revalidate.

to it, so that we say we will do the wrapping just once right here
in _execute_context() / _execute_default().  An adjustment is made
to _handle_dbapi_error() to not assume self.__connection in case
we are already in an invalidated state

further adjustment to
0639c199a547343d62134d2f233225fd2862ec45, 41e7253dee168b8c26c49, #3266

when you call :meth:`.Connection.connect`, would not share transaction
status with the parent.  The architecture of branching has been tweaked
a bit so that the branched connection defers to the parent for
all transactional status and operations.
fixes #3190

when you call :meth:`.Connection.connect`, would not share invalidation
status with the parent.  The architecture of branching has been tweaked
a bit so that the branched connection defers to the parent for
all invalidation status and operations.
fixes #3215

- Fixed bug which would occur if a DBAPI exception
occurs when the engine first connects and does its initial checks,
and the exception is not a disconnect exception, yet the cursor
raises an error when we try to close it.  In this case the real
exception would be quashed as we tried to log the cursor close
exception via the connection pool and failed, as we were trying
to access the pool's logger in a way that is inappropriate
in this very specific scenario. fixes #3063

Found using: https://github.com/intgr/topy