Xor is complementary-arg aware
Equivalent is complementary-arg aware
8413: Min and Max are floor and ceiling aware

- facilitate changes with reversed property of Relational which
  reverses the direction of the Relational
special-case +/-oo in _Inequality
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
quick