Make inequalities behave the same as their operators when infinity is involved.

Previously, Lt(x, oo) would not evaluate, while x < oo would return True.
Tests for this (marked XFAIL) were added in pull request #7783.  Now, all
inequality classes (Lt, etc.) will harness the same code behind the operators
(<, etc.) whenever positive or negative infinities are involved, guaranteeing
that the two produce identical results.

Note that the test in question has not had its XFAIL removed, as pi > x does
not yet behave the same as Gt(pi, x).  Once this is corrected too, the test
will pass.