Allow manually specifying which migrations to run

[vpontis]

Right now when I run db:migrate or db:migrate:undo it either tries to do run all migrations or undo all migrations.

It might be nice to have a --to [time] flag on both ways that will stop running migrations past that time.

[mwdhouse]

The fact that the documentation states that db:migrate:undo will undo the last migration done, when it in fact undoes all migrations, is either a really big bug or I am misunderstanding.

[mickhansen]

@chrisatsc it's a bug.

[sdepold]

This ticket should be fixed by now. Please re-open it if its still an issue.