evaluate 'diff3 -E' vs. 'diff3 -A'

We're currently passing -A to diff3, which gives us beautiful 3-way conflict
markers.  (Well, *I* love them, anyway).

Someone has pointed out that this feature is buggy...?  That in fact redundant
patches are detected as such, and still marked off with conflict markers.  Let's
investigate this, and see if we need to switch back to -E instead.