merge-recursive: Avoid excessive output for and reprocessing of renames

merge-recursive: Avoid excessive output for and reprocessing of renames

In 5a2580d (merge_recursive: Fix renames across paths below D/F conflicts
2010-07-09) and ae74548 (merge-recursive: Fix multiple file rename across
D/F conflict 2010-08-17), renames across D/F conflicts were fixed by
making process_renames() consider as unprocessed renames whose dst_entry
"still" had higher stage entries.  The assumption was that those higher
stage entries would have been cleared out of dst_entry by that point in
cases where the conflict could be resolved (normal renames with no D/F
conflicts).  That is not the case -- higher stage entries will remain in
all cases.

Fix this by checking for higher stage entries corresponding to D/F
conflicts, namely that stages 2 and 3 have exactly one nonzero mode between
them.  The nonzero mode stage corresponds to a file at the path, while the
stage with a zero mode will correspond to a directory at that path (since
rename/delete conflicts will have already been handled before this codepath
is reached.)

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>