MySQL: Empty `where` param makes bogus query.

Added failing MySQL tests for SelectQuery when the `where` is all kinds of empty.
Now it returns `1=1` if nothing else, as suggested by @muka.
Merge branch 'nowhere_is_empty' of git://github.com/terraflubb/sequelize into terraflubb-nowhere_is_empty
Merge branch 'master' of github.com:sequelize/sequelize
fixed specs
Merge branch 'terraflubb-nowhere_is_empty'