Potential fix for #1057

Tests for the undo flag would definitely be a good idea, too.
Merge branch 'issue_1057' of https://github.com/elliotf/sequelize into elliotf-issue_1057

Conflicts:
	bin/sequelize
run undo tests for the flags "--undo" and "-u" as well
sequelize --undo
Merge branch 'master' into milestones/2.0.0