Added AssumeSymGT, AssumeSymGE, AssumeSymLT, AssumeSymLE to add some minor improvements to path-sensitivity.  Right now we basically treat 'x > y' and 'x < y' as implying 'x != y', but this restriction will only inevitably apply to our must rudimentary value tracking component (we'll implement more advanced value reasoning later).

llvm-svn: 54493