detailed information on unmerged paths.
For an unmerged path, instead of recording a single mode/SHA1 pair,
-the dircache records up to three such pairs; one from tree O in stage
+the index records up to three such pairs; one from tree O in stage
1, A in stage 2, and B in stage 3. This information can be used by
the user (or the porcelain) to see what should eventually be recorded at the
path. (see git-read-tree for more information on state)