In my tests, I'm finding that declaring iterators in terms of ranges can sometimes have dangerous side-effects where the range temporary is destroyed, taking the underlying iterators out with it.

This changes the iterators so that they are no longer implemented in terms of ranges (so it's a very partial revert of the existing rangification efforts).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203299 91177308-0d34-0410-b5e6-96231b3b80d8