Merge branch 'ak/protect-any-current-branch'

"git fetch" without the "--update-head-ok" option ought to protect
a checked out branch from getting updated, to prevent the working
tree that checks it out to go out of sync.  The code was written
before the use of "git worktree" got widespread, and only checked
the branch that was checked out in the current worktree, which has
been updated.
(originally called ak/fetch-not-overwrite-any-current-branch)

* ak/protect-any-current-branch:
  branch: protect branches checked out in all worktrees
  receive-pack: protect current branch for bare repository worktree
  receive-pack: clean dead code from update_worktree()
  fetch: protect branches checked out in all worktrees
  worktree: simplify find_shared_symref() memory ownership model
  branch: lowercase error messages
  receive-pack: lowercase error messages
  fetch: lowercase error messages

diff --cc builtin/notes.c
Simple merge

diff --cc builtin/receive-pack.c
Simple merge

diff --cc t/t5516-fetch-push.sh
Simple merge