Inequalities: return BooleanAtoms instead of bools.

Extension of a similar change to Relational objects.  Now any usage of <, <=,
>, or >= will result in a BooleanAtom (S.true or S.false) being returned.
To handle this, many pieces of code were changed so they no longer expect True
or False; some downstream code may need similar treatment.
Merge pull request #2984 from Tempel/number_ineq_STrue

Inequalities: return BooleanAtoms instead of bools.