migrations gotcha

Just wanted to share this gotcha:

   1. Create model A and initialize some record from
      within the very migration.
   2. Create model B (perhaps 27 migrations later,
      two weeks later).
   3. An observer of A uses B.

Now you can't do a fresh install (or go down to VERSION corresponding to 1. and then up).

-- fxn

Why? I see no bug there. It is just a consequence of how things work.

-- fxn