put Number on rhs when simplifying Relational

This will allow any test to be written as 0 < x or x > 0 since the former
will turn into the latter by Python rules (unless S(0) < x is written).
do not evaluate in reversed
rework connectivity testing; watch for evaluation
do not accept serendipitous evaluation in And/Or
add coverage tests
make Number on rhs part of Relational.canonical
quick