That is, after exhausing all rows using the fetch methods, the
DBAPI cursor is released as before and the object may be safely
discarded, but the fetch methods may continue to be called for which
they will return an end-of-result object (None for fetchone, empty list
for fetchmany and fetchall).   Only if :meth:`.ResultProxy.close`
is called explicitly will these methods raise the "result is closed"
error.
fixes #3330 fixes #3329

The "wrapping" employed by the mssql and oracle dialects using the
"iswrapper" argument was not being used intelligently by the compiler,
and the result map was being written incorrectly, using
*more* columns in the result map than were actually returned by
the statement, due to "row number" columns that are inside the
subquery.   The compiler now writes out result map on the
"top level" select in all cases
fully, and for the mssql/oracle wrapping case extracts out
the "proxied" columns in a second step, which only includes
those columns that are proxied outwards to the top level.

This change might have implications for 3rd party dialects that
might be imitating oracle's approach.   They can safely continue
to use the "iswrapper" kw which is now ignored, but they may
need to also add the _select_wraps argument as well.

such that they are matched to the received result set positionally,
rather than by name.  Originally, this was seen as a way to handle
cases where we had columns returned with difficult-to-predict names,
though in modern use that issue has been overcome by anonymous
labeling.   In this version, the approach basically reduces function
call count per-result by a few dozen calls, or more for larger
sets of result columns.  The approach still degrades into a modern
version of the old approach if textual elements modify the result
map, or if any discrepancy in size exists between
the compiled set of columns versus what was received, so there's no
issue for partially or fully textual compilation scenarios where these
lists might not line up.  fixes #918
- callcounts still need to be adjusted down for this so zoomark
tests won't pass at the moment

with :meth:`.Connection.execution_options` when a :class:`.Transaction`
is in play; DBAPIs and/or SQLAlchemy dialects such as psycopg2,
MySQLdb may implicitly rollback or commit the transaction, or
not change the setting til next transaction, so this is never safe.
- Added new parameter :paramref:`.Session.connection.execution_options`
which may be used to set up execution options on a :class:`.Connection`
when it is first checked out, before the transaction has begun.
This is used to set up options such as isolation level on the
connection before the transaction starts.
- added new documentation section
detailing best practices for setting transaction isolation with
sessions.
fixes #3296

logic to some degree in DefaultExecutionContext.  In particular
we are removing post_insert() which doesn't appear to be used
based on a survey of prominent third party dialects.  Callcounts
aren't added to existing execute profiling tests and inserts might be
a little better.
- simplify the execution_options join in DEC.  Callcounts don't
appear affected.

repaired to work more usefully with tables that have Python-
side default values and/or functions, as well as server-side
defaults. The feature will now work with a dialect that uses
"positional" parameters; a Python callable will also be
invoked individually for each row just as is the case with an
"executemany" style invocation; a server- side default column
will no longer implicitly receive the value explicitly
specified for the first row, instead refusing to invoke
without an explicit value. fixes #3288