Patch by Ben Laurie:

ConstraintManager:
- constify getSymVal()

BasicConstraintManager:
- Pull out logic that would be common to ConstraintManagers of a similar nature
  and put them in a parent class called 'SimpleConstraintManager'.

RangeConstraintManager:
- Added a new prototype ConstraintManager to track ranges of variables! This
  ConstraintManager keeps tracks of ranges of concrete integers that a symbolic
  integer may have.

AnalysisConsumer:
- Add driver option to use RangeConstraintManager with GRExprEngine-based
  analyses.

llvm-svn: 64558