Added a path-sensitive idempotent operation checker (-analyzer-idempotent-operation...

Added a path-sensitive idempotent operation checker (-analyzer-idempotent-operation). Finds idempotent and/or tautological operations in a path sensitive context, flagging operations that have no effect or a predictable effect.

Example:
{
int a = 1;
int b = 5;
int c = b / a; // a is 1 on all paths
}

- New IdempotentOperationChecker class
- Moved recursive Stmt functions in r107675 to IdempotentOperationChecker
- Minor refactoring of SVal to allow checking for any integer
- Added command line option for check
- Added basic test cases

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107706 91177308-0d34-0410-b5e6-96231b3b80d8