relational ops: Don't use False as a replacement for 'other', if we can't sympify 'other'

Unfortunately, we can't use _sympifyit decorator, because in py2 class
instances are compared by object identity ("address") if no other
comparison helpers are defined.

fixes #7833

How about this as well?
raises(TypeError, lambda: op(bar, a))

(I know your fixes are for when `other` is not `_sympify`-able, but other way around should raise the error too.)