Re: [PATCH 19/30] merge-recursive: Split out code for determining diff_filepairs

Elijah Newren [off-list ref] writes:

Create a new function, get_diffpairs() to compute the diff_filepairs
between two trees.  While these are currently only used in
get_renames(), I want them to be available to some new functions.  No
actual logic changes yet.

OK.  

This refactors an easy-to-use (in the context of merge-recursive
code) wrapper to diff-tree out of the existing code, which makes
sense.