Merge branch 'es/do-not-let-rebase-switch-to-protected-branch'

"git rebase BASE BRANCH" rebased/updated the tip of BRANCH and
checked it out, even when the BRANCH is checked out in a different
worktree.  This has been corrected.

* es/do-not-let-rebase-switch-to-protected-branch:
  rebase: refuse to switch to branch already checked out elsewhere
  t3400: make test clean up after itself

diff --cc builtin/rebase.c
Simple merge

diff --cc t/t3400-rebase.sh
Simple merge