stopgap fix for contrib.sql_server - review comment pls

I don't sql-server to test against, is it possible to remove this in
favor of https://bitbucket.org/Manfre/django-mssql which is still in
active development? (the version in contrib seems like an older version
of the django-mssql module)
temporary debugging statements to track down 2 problems

1) storage.tests.pseudostreaming is the only test failing (it may be
due to #2, but it looks like the way Client behaves is now different,
so it's not retrieving the file 'test url for
2) OperationalError: (1061, "Duplicate key name
'access_accesscontrol_846f0221'"), which emits from
access.middleware.AccessOnStart, which is weird because as far as I can
tell that class exists to
run once (it actually seems like it should only run once on startup,
actually) - it triggers several tracebacks if run with
`ROOIBOS_ADDITIONAL_SETTINGS=config.settings_test python manage.py test
-v 2 --traceback
rooibos.storage.tests.PseudoStreamingStorageSystemTestCase`, but it
never displays the log message I added for the sql execution.
implement multi-file requirements pattern

the idea being, for example, `pip install requirements/base.txt` for a
server but `pip install requirements/dev.txt` for developers (to keep
libraries like mock and nose, etc away from production servers)
improve settings_test file

suppress south migrations from running, document reason for forcing
INNODB on mysql, adding a warning in the event someone tries to run a
server with settings_test active.

Not really the most exciting commit ever, actually.