Merge branch 'pw/rebase-of-a-tag-fix'

"git rebase <upstream> <tag>" failed when aborted in the middle, as it mistakenly tried to write the tag object instead of peeling it to HEAD. * pw/rebase-of-a-tag-fix: rebase: dereference tags rebase: use lookup_commit_reference_by_name() rebase: use our standard error return value t3407: rework rebase --quit tests t3407: strengthen rebase --abort tests t3407: use test_path_is_missing t3407: rename a variable t3407: use test_cmp_rev t3407: use test_commit t3407: run tests in $TEST_DIRECTORY