emitted for the "_cursor_execute()" method of :class:`.Connection`;
this is the "quick" executor that is used for things like
when a sequence is executed ahead of an INSERT statement, as well as
for dialect startup checks like unicode returns, charset, etc.
the :meth:`.ConnectionEvents.before_cursor_execute` event was already
invoked here.  The "executemany" flag is now always set to False
here, as this event always corresponds to a single execution.
Previously the flag could be True if we were acting on behalf of
an executemany INSERT statement.

:func:`.attributes.flag_modified` where the change event would not be
propagated if the attribute had been reassigned to itself.
fixes #2997

against a non-selectable, such as a :func:`.literal_column`, and then
an attempt was made to use :meth:`.Query.join` such that the "left"
side would be determined as ``None`` and then fail.  This condition
is now detected explicitly.

flag for :func:`.event.listen` to work with mapper / instance events.

"true" / "false" or "1" / "0".
- added Boolean tests to the test suite

SQLA internal tests outside; plus things like savepoints, twophase

and adding some more requirements

apply to :class:`.CheckConstraint` objects that are associated
directly with a :class:`.Column` instead of just on the
:class:`.Table`.

where the name of a check constraint making use of the
`"%(constraint_name)s"` token would get doubled up for the
constraint generated by a boolean or enum type, and overall
duplicate events would cause the `"%(constraint_name)s"` token
to keep compounding itself.
fixes #2991