has_units, UnitArray and UnitScalar have moved from BlockCanvas to SciMath
I've moved has_units, UnitArray and UnitScalar from BlockCanvas's
enthought.numerical_modeling.units namespace to SciMath's
enthought.units namespace. The only affected ETS packages, as far as I
could find, were BlockCanvas, SciMath and CodeTools, all of which have
been updated. If there are any problems I didn't catch, let me know.