yt Answer Testing

This is where answer testing for yt is set up.  The idea is that you should be
able to go into this directory and run:

    enzo_test store SOMENAME *.py

and it will run all the tests inside the *.py files.  SOMENAME should probably
be the current changeset hash.  All the parameter files located in OutputLog
will be passed into the load() function, the tests will be run, answers stored,
and then

    enzo_test compare OTHERNAME SOMENAME *.py

will compare the two results.

Currently it is not parallel-safe.

The idea is that once we have some set of tests, we can execute this on every
couple changesets, see the results, and then determine whether or not we have
ultimately succeeded in creating a stable code.