Alias db:migrate to dm:migrate and ar:migrate.
Also alias db:migrate to sq:migrate.
Alias sq:migrate to sq:migrate:up.
Alias db:migrate to sq:migrate as well (issue #1036).
Also alias db:migrate to mr:migrate (issue #1036).
Merge pull request #1036 from postmodern/alias_db_migrate_tasks

Alias db:migrate to dm:migrate and ar:migrate.