Remove old constraints and scripts

They don't work anymore (because I've changed the semantics), so I'll
be writing new ones.
Minor cleanups

 * Fix regexp for < 10% coverage
 * Reorganize some imports
 * Some renamed functions in Constraint
 * Adjusted Constraint.propagate() to avoid == comparisons
 * Remove some stuff I didn't like from Constraint
 * Removed Store.impose()   (it'll be back)
 * Made Store.IntVar/BoolVar a bit smarter
 * IntVar: only propagate if domain actually changed
 * Modified IntVar.__str__()
 * Sprinkled a few TODO comments here and there
100% test coverage for types.py

Also removed a stray Z.
Added IntVar.boolvalue

Will be True/False if that is determined, otherwise None.
Minor improve to name change test

Make sure that new variables can use the discarded name.
BitwiseAnd constraint

Lots of bit fiddling... fun, but easy to mess up! :)