Changed GRExprEngine to pass down a reference to itself when checkers are doing posta...

Changed GRExprEngine to pass down a reference to itself when checkers are doing postanalysis. This allows the checker to gather information about the state of the engine when it has finished.
- Exposed the worklist and BlockAborted flag in GRCoreEngine
- Changed postanalysis checkers to use the new infrastructure

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@110095 91177308-0d34-0410-b5e6-96231b3b80d8