GRStateManager.  Having these references was an abstraction violation,
as they really should only be known about GRExprEngine.

This change required adding a new 'ProcessAssume' callback in
GRSubEngine.  GRExprEngine implements this callback by calling
'EvalAssume' on all registered Checker objects as well as the
registered GRTransferFunc object.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@92549 91177308-0d34-0410-b5e6-96231b3b80d8