Split databaseTest into separate tests by reaction family.

It uses test generators, a feature of nose, which means we
can't use the built-in unittest module any more, but that's OK
because we were using nose anyway.  You can use nosetests, or 
just run it on its own:

 $ python databaseTest.py
Merge pull request #238 from rwest/dbtest

Split databaseTest into separate tests by reaction family.