Fix performance regression for partial commits
Fix performance regression for partial commits

When running "git commit paths" to create a partial commit, we
used to carefully build the temporary index so that we do not
lose the cached stat information.  The rewrite of the command in
C lost it by carelessly using read_tree().

This resurrects the earlier behaviour to keep the cached stat
information as much as possible by using one-tree merge logic.

Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git