Exclude unifying outputs in coverage checker.

Now,
TEST/unique-bug.elf:35.10-35.11 Error:
Coverage error --- missing cases:
{X1:tpe} {X2:tpe} {X3:tlookup X1 X2} {X4:tpe} {X5:tpe} {X6:tlookup X4 X5}
   |- lookup-restrict tl/id tl/id X3 X6,
{X1:tpe} {X2:tpe} {X3:tlookup X1 X2} {X4:tpe} {X5:tpe} {X6:tlookup X4 X5}
   |- lookup-restrict tl/id tl/id X3 X6.
add test case, but how to auto-test failures?
Merge pull request #2 from namin/unique-fix

Exclude unifying outputs in coverage checker.
Transfer Mlton build over to mlb files, as they've been asking us to do for years and now insist on.