Comment 2 for bug 90569

Actually we could generalize this idea and do a 2-way merge: if the two files are identical, it behaves as the OP wants, and otherwise you get a new file with some conflicts.
It may not always be a good idea, but at least in my use case, it would DTRT in 99% of the cases since conflicts between new versioned files and pre-existing unversioned files are almost always due to a change where a file becomes versioned.