number of columns we're actually reporting on
- add more tests for negative row index
- changelog/migration

:meth:`.ConnectionEvents.detach`,
:meth:`.ConnectionEvents.close_detached`.

via :paramref:`.create_engine.isolation_level` and
:paramref:`.Connection.execution_options.isolation_level`
parameters.  fixes #3534

for example an exception object made within a test suite can
still repr (error seen in Keystone)

logging, exception, and  ``repr()`` purposes now truncate very large
scalar values within each collection, including an
"N characters truncated"
notation, similar to how the display for large multiple-parameter sets
are themselves truncated.
fixes #2837

the warning here to all safe_reraise() cases in Python 2.
- Revisiting :ticket:`2696`, first released in 1.0.10, which attempts to
work around Python 2's lack of exception context reporting by emitting
a warning for an exception that was interrupted by a second exception
when attempting to roll back the already-failed transaction; this
issue continues to occur for MySQL backends in conjunction with a
savepoint that gets unexpectedly lost, which then causes a
"no such savepoint" error when the rollback is attempted, obscuring
what the original condition was.

The approach has been generalized to the Core "safe
reraise" function which takes place across the ORM and Core in any
place that a transaction is being rolled back in response to an error
which occurred trying to commit, including the context managers
provided by :class:`.Session` and :class:`.Connection`, and taking
place for operations such as a failure on "RELEASE SAVEPOINT".
Previously, the fix was only in place for a specific path within
the ORM flush/commit process; it now takes place for all transational
context managers as well.
fixes #2696