Added psuedo-constant analysis and integrated it into the false positive reduction...

Added psuedo-constant analysis and integrated it into the false positive reduction stage in IdempotentOperationChecker.
- Renamed IdempotentOperationChecker::isConstant to isConstantOrPseudoConstant to better reflect the function
- Changed IdempotentOperationChecker::PreVisitBinaryOperator to only run 'CanVary' once on undefined assumptions
- Created new PsuedoConstantAnalysis class and added it to AnalysisContext
- Changed IdempotentOperationChecker to exploit the new analysis
- Updated tests with psuedo-constants
- Added check to IdempotentOperationChecker to see if a Decl is const qualified

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@111426 91177308-0d34-0410-b5e6-96231b3b80d8