Extended Description

r171828 introduces a regression where ARCMT uses a std::list iterator after invalidation. From the email thread:

"The use of iterators here is problematic because
handleProtectedScopeError can invalidate the iterators. This is
causing a failed assertion in debug build of MSVC11 where there are
checked iterators involved.

From what I am seeing, handleProtectedScopeError has a Transaction
object, which on destruction winds up calling
CapturedDiagList::clearDiagnostic, and that calls erase on the list,
which invalidates the iterators. Attempting to perform the comparison
then fires the assert.

I'm not entirely certain of the best way to solve this issue, but I
figured I would mention that it causes problems. We have a test case
already demonstrating the issue with test\ARCMT\protected-scope.m"