Merge pull request #7861 from skirpichev/oo-ineq

Refactor processing of inequalities with oo
UnXFAIL test_inequalities_symbol_name_same

1. return unevaluated Relational in the __gt__/__ge__ helpers
   of the Number class
2. Relational._eval_sides fallback to _eval_relation(lhs, rhs)
   if diff is nan (e.g. oo - oo)