restage pointer file after unlock

This avoids a later git status or similar taking a long time to run
as it runs git-annex smudge once per file. While v9 repositories do
avoid that taking long when the files are small, large files can still
make git status take a very long time.

This does make unlock slower, because now git-annex smudge is being run
once per file unlocked. However, the next commit should speed that up in
many cases.

Sponsored-by: Boyd Stephen Smith Jr. on Patreon

doc/todo/git_status_smudges_unncessarily_after_unlock.mdwn

@@ -12,3 +12,25 @@ commit -a`). Afterwards, `git status` then smudged it again, unsure why!
 --[[Joey]]
 
 [[!tag confirmed]]
+
+> I wondered if this was still a problem in a v9 repository with
+> filter-process used instead of smudge. It's not really -- after unlocking
+> 1000 files, git status did need to refresh all 1000, but it ran
+> relatively quickly because it was able to use filter-process.
+> 
+> But, those were small files. Large files would make it slower as it pipes
+> their content though. It would be better for Command.Unlock to use 
+> restagePointerFile, so whatever price there is is paid during unlocking
+> and not unexpectedly later on.
+> 
+> I tried again making Command.Unlock use restagePointerFile, and this
+> slowed git-annex unlock. But git status did then avoid doing any more
+> smudgeing. It seems that each call to restagePointerFile is running
+> git update-index, so still one git-annex smudge per file, rather
+> than combining several together.
+> 
+> That's because restagePointerFile uses the git queue, and unlock 
+> also queues a git add or something, so the queue isn't able to built
+> up because two dissimilar things are being queued. This seems an
+> unncessary behavior; it could queue up all the git adds and then
+> run restagePointerFile after them all.