Add develover sql switch

Add develover sql switch

If you want to play with the current state of sql, you need
a switch to turn it on. So here is the super secret
developer switch.

So you want to know where it is?

Here it is:

Create a file mediagoblin/db/sql_switch.py and put one line
in it: "use_sql = True" (or False to disable again). Right,
that's it. If you want to delete it, remember to delete the
*.pyc too.

Be careful not to "git add" it by accident!