* Has a couple of limitations - won't check deferred context or
NO_OVERWRITE Map()s except in a captured frame. This could in theory be
implemented but it'd be complex and I don't want to complicate/break
the normal path.
* When an overrun is detected, a messagebox pops up to block the thread,
and if you hit yes, it will debugbreak.
baldurk
56e7f0c754