Added ability to report incorrect coordinates in point and vector
answers, and incorrect endpoints and endpoint types in intervals.
Separated these kinds of checks from the typeMatch check, where they
didn't really belong.
Added ability to specify intervals and unions as strings in Interval()
and Union(), which makes it easier to make constants of these types.
There are still problems comparing intervals that contain infinities;
I really need to make the infinity object to solve this, so have put
off trying to fix that for now.