[Ruby] Parallel migration

[BenJamin Prater]

I can't imagine needing to alter tables on a continual basis. Wouldn't
this be a one-shot deal where you could live with the time necessary
to alter the table?

Even if you could parallel alter (you could always do this on the
command line and bypass migrations), it may not go any quicker since
your cpu is going to be fairly saturated by the previous request.

Ben