Fix MSSQL dialects visit_drop_index to use the correct DDL
fix underline
- add a new example section for "join conditions", start putting
the primaryjoin examples there
Merged in dharland/sqlalchemy/patch-mssql-drop-index (pull request #7)

Fix MSSQL dialects visit_drop_index to use the correct DDL
- changelog + test for pullreq #7, MSSQL dialect for DROP INDEX
- The precedence rules for the :meth:`.ColumnOperators.collate` operator
have been modified, such that the COLLATE operator is now of lower
precedence than the comparison operators.  This has the effect that
a COLLATE applied to a comparison will not render parenthesis
around the comparison, which is not parsed by backends such as
MSSQL.  The change is backwards incompatible for those setups that
were working around the issue by applying :meth:`.Operators.collate`
to an individual element of the comparison expression,
rather than the comparison expression as a whole. [ticket:2879]
- Made a slight adjustment to the logic which waits for a pooled
connection to be available, such that for a connection pool
with no timeout specified, it will every half a second break out of
the wait to check for the so-called "abort" flag, which allows the
waiter to break out in case the whole connection pool was dumped;
normally the waiter should break out due to a notify_all() but it's
possible this notify_all() is missed in very slim cases.
This is an extension of logic first introduced in 0.8.0, and the
issue has only been observed occasionally in stress tests.
- The :class:`.QueuePool` has been enhanced to not block new connection
attempts when an existing connection attempt is blocking.  Previously,
the production of new connections was serialized within the block
that monitored overflow; the overflow counter is now altered within
it's own critical section outside of the connection process itself.
[ticket:2880]
- restore having the connection closed before decrementing the overflow counter
- A DBAPI that raises an error on ``connect()`` which is not a subclass
of dbapi.Error (such as ``TypeError``, ``NotImplementedError``, etc.)
will propagate the exception unchanged.  Previously,
the error handling specific to the ``connect()`` routine would both
inappropriately run the exception through the dialect's
:meth:`.Dialect.is_disconnect` routine as well as wrap it in
a :class:`sqlalchemy.exc.DBAPIError`.  It is now propagated unchanged
in the same way as occurs within the execute process. [ticket:2881]
- add tests for this in test_parseconnect, but also add tests in test_execute
to ensure the execute() behavior as well
- remove verbiage about "namespaces" from the dogpile example, [ticket:2862]
- fix broken py2k/py3k isms
specify run as module here
- documentation cleanup in ORM including [ticket:2816]
- The :func:`.engine_from_config` function has been improved so that
we will be able to parse dialect-specific arguments from string
configuration dictionaries.  Dialect classes can now provide their
own list of parameter types and string-conversion routines.
The feature is not yet used by the built-in dialects, however.
[ticket:2875]