redundant tests

[Stephen Weeks]

Here is a comparison of mlton built with and without redundant tests.  I give
the code size and the time to compile itself (with redundant tests, but that's
irrelevant). 

	without 	with
size	7457580		7450964
time	532		534

Anyways, no great change.  I obviously need to put in stuff about transitivity
and simple algebra (e.g. i + 1 < i + 2).

Something I did lately has added about 0.8M to the size of mlton-compile.  I'm
not sure what it was, but it appears to be unrelated to redundant test
elimination.  It might have been CSE, which increased live ranges.