fixed migrations bug from issue #1829, down migrations now operate only on completed migrations
complies with "use strict;" tests passing
fixed failing test on postgres
Merge branch 'master' of https://github.com/sequelize/sequelize
Comply with use strict (aka semicolins are fun and profitable)
Merge pull request #2300 from jtschoonhoven/master

Fix for issue #1829: down migrations operate only on *completed* migrations