Changed the method name PtrState.IsKnownIncremented() to PtrState.HasKnownPositiveRefCount().

Now said method matches namewise every other method which refers to
the member KnownPositiveRefCount of the class PtrState.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177816 91177308-0d34-0410-b5e6-96231b3b80d8