Interval._intersect handles (-oo, oo)

If the other Interval has a real or infinite value in it then
it will be contained within (-oo, oo).
make sure solve/reduce_inequalities can handle the bare inequality

Although this worked in master,

>>> solve(sin(x)>S.Half,x)
And(pi/6 < x, x < 5*pi/6)

This did not:

>>> solve(sin(x)>S.Half)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "sympy\solvers\solvers.py", line 692, in solve
    return reduce_inequalities(f, symbols=symbols)
  File "sympy\solvers\inequalities.py", line 517, in reduce_inequalities
    raise NotImplementedError("can't reduce %s" % inequalities)

Now it does.