better Or implied checking, unit tests

Partial fix for performance problems noted in the following bugs:
http://bugs.racket-lang.org/query/?cmd=view&pr=14825
http://bugs.racket-lang.org/query/?cmd=view&pr=14838

Both of these bugs are largely due to propositions unnecessarily growing exponentially. (Information was being duplicated and recorded numerous times in slightly different, logically weaker propositions. These redundancies are now detected by the 'filter-ops.rkt' function 'implied-atomic?'.)

The additional fix involving removing implication propositions is not an across the board improvement w/o let-aliasing, so I'm planning on submitting it in conjunction w/ let-aliasing.