Fix: <rdar://problem/7275774> Static analyzer warns about NULL pointer when

                              adding assert

This fix required a few changes:

SimpleSValuator:
- Eagerly replace a symbolic value with its constant value in EvalBinOpNN
  when it is constrained to a constant.  This allows us to better constant fold
  values along a path.
- Handle trivial case of '<', '>' comparison of pointers when the two pointers
  are exactly the same.

RegionStoreManager:

llvm-svn: 83358