Remove tables from metadata when autoload fails

If autoloading of a table fails, don't register it in a metadata
instance. It seems that the original behaviour was accidentally
changed in f6198d9abf453182f4b111e0579a7a4ef1614e79, restore it.

Closes issue #2988
Add is_ and isnot filter to the tutorial

Most linter complain when comparing with None.
Merge branch 'ca/dev/add_is_and_isnot_to_tutorial' of https://github.com/charlax/sqlalchemy
- Fixed bug in mutable extension as well as
:func:`.attributes.flag_modified` where the change event would not be
propagated if the attribute had been reassigned to itself.
fixes #2997
fix assertion
- The :meth:`.ConnectionEvents.after_cursor_execute` event is now
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.
- reword the paragraph which talks about web framework integration for sessions:

1. fix the typo in the paragraph, fixes #2998
2. as zope-sqlalchemy only provides transaction integration and not session scoping,
dial back the language here as people are probably using scoped_session with pyramid anyway
3. as I'm going to again start recommending people don't cling to flask-sqlalchemy so hard,
take out the word "strongly" from the recommendation.
4. as flask is the only framework I can think of that actually has an explicit SQLAlchemy
layer that handles setting up scoped_session, take out the word "most", now it's "some web frameworks"
(by which it means "only flask...and flask-sqlalchemy is probably not worth using anyway")
Fix tag typo in changelog_09
Merge pull request #81 from tony/patch-2

Fix tag typo in changelog_09
Merge branch 'fix_table_registration' of https://github.com/malor/sqlalchemy into t
changelog to fix #2988
- Adjusted ``setup.py`` file to support the possible future
removal of the ``setuptools.Feature`` extension from setuptools.
If this keyword isn't present, the setup will still succeed
with setuptools rather than falling back to distutils.  C extension
building can be disabled now also by setting the
DISABLE_SQLALCHEMY_CEXT environment variable.  This variable works
whether or not setuptools is even available. fixes #2986
- using platform.python_implementation() in setup.py to detect CPython.
I've tested this function on OSX and linux on Python 2.6 through 3.4,
including 3.1, 3.2, 3.3.
Unfortunately, on OSX + 3.2 only, it seems to segfault.  I've tried
installing 3.2.5 from the python.org .dmg, building it from source,
and also blew away the whole 3.2 directory, something seems to be wrong
with the "platform" module on that platform only, and there's also no
issue on bugs.python.org; however, I'm going with
it anyway. If someone is using 3.2 on OSX they really should be upgrading.
- we aren't supporting py2.5 so just simplify this import for platform, re: #2986
- Added new datatype :class:`.oracle.DATE`, which is a subclass of
:class:`.DateTime`.  As Oracle has no "datetime" type per se,
it instead has only ``DATE``, it is appropriate here that the
``DATE`` type as present in the Oracle dialect be an instance of
:class:`.DateTime`.  This issue doesn't change anything as far as
the behavior of the type, as data conversion is handled by the
DBAPI in any case, however the improved subclass layout will help
the use cases of inspecting types for cross-database compatibility.
Also removed uppercase ``DATETIME`` from the Oracle dialect as this
type isn't functional in that context.  fixes #2987
- A major improvement made to the mechanics by which the :class:`.Engine`
recycles the connection pool when a "disconnect" condition is detected;
instead of discarding the pool and explicitly closing out connections,
the pool is retained and a "generational" timestamp is updated to
reflect the current time, thereby causing all existing connections
to be recycled when they are next checked out.   This greatly simplifies
the recycle process, removes the need for "waking up" connect attempts
waiting on the old pool and eliminates the race condition that many
immediately-discarded "pool" objects could be created during the
recycle operation. fixes #2985
- Fixed a few errant ``u''`` strings that would prevent tests from passing
in Py3.2.  Patch courtesy Arfrever Frehtes Taifersar Arahesis. fixes #2980
- restore the old behavior of the connection pool replacing itself just
within userland engine.dispose(); as some SQLA tests already failed when the replace step
was removed, due to those conns still being referenced, it's likely this will
create surprises for all those users that incorrectly use dispose()
and it's not really worth dealing with.  This doesn't affect the change
we made for ref: #2985.
there's no "assert_call_count" on mock
- An event listener can now be associated with a :class:`.Engine`,
after one or more :class:`.Connection` objects have been created
(such as by an orm :class:`.Session` or via explicit connect)
and the listener will pick up events from those connections.
Previously, performance concerns pushed the event transfer from
:class:`.Engine` to  :class:`.Connection` at init-time only, but
we've inlined a bunch of conditional checks to make this possible
without any additional function calls. fixes #2978
- Fixed regression from 0.8.3 as a result of :ticket:`2818`
where :meth:`.Query.exists` wouldn't work on a query that only
had a :meth:`.Query.select_from` entry but no other entities.
re: #2818 fixes #2995