Should migrations require presence of psql/mysql command line clients?

[repeatingbeats]

I'd prefer to not require psql in the environments that I run migrations from, as some environments (e.g. Heroku dynos) don't allow arbitrary installation of command line dependencies. Would you be open to a pull request that uses the pg JS client instead of spawning a psql process? I'm happy to do so, but figured it would be a good idea to get some feedback as to whether you're interested in such a change and if you have any other thoughts on implementation. Thanks.

[mgutz]

Please submit. I'll add an argument --driver pg to override the default.