ProgramPoint:

- Added four new ProgramPoint types that subclass PostStmt for use in
  GRExprEngine::EvalLocation:
  - PostOutOfBoundsCheckFailed
  - PostUndefLocationCheckFailed
  - PostNullCheckFailed
  - PostLocationChecksSucceed
  These were created because of a horribly subtle caching bug in EvalLocation
  where a node representing an "bug condition" in EvalLocation (e.g. a null
  dereference) could be re-used as the "non-bug condition" because the Store did
  not contain any information to differentiate between the two. The extra
  program points just disables any accidental caching between EvalLocation and
  its callers.

GRExprEngine:
- EvalLocation now returns a NodeTy* instead of GRState*.  This should be used as the "vetted" predecessor for EvalLoad/EvalStore.

llvm-svn: 61105