revert: do not remove state until sequence is finished

As v1.7.8-rc0~141^2~4 (2011-08-04) explains, git cherry-pick removes
the sequencer state just before applying the final patch.  In the
single-pick case, that was a good thing, since --abort and --continue
work fine without access to such state and removing it provides a
signal that git should not complain about the need to clobber it ("a
cherry-pick or revert is already in progress") in sequences like the
following:

	git cherry-pick foo
	git read-tree -m -u HEAD; # forget that; let's try a different one
	git cherry-pick bar

After the recent patch "allow single-pick in the middle of cherry-pick
sequence" we don't need that hack any more.  In the new regime, a
traditional "git cherry-pick <commit>" command never looks at
.git/sequencer, so we do not need to cripple "git cherry-pick
<commit>..<commit>" for it any more.

So now you can run "git cherry-pick --abort" near the end of a
multi-pick sequence and it will abort the entire sequence, instead of
misbehaving and aborting just the final commit.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -1018,18 +1018,8 @@ static int pick_commits(struct commit_list *todo_list, struct replay_opts *opts)
 	for (cur = todo_list; cur; cur = cur->next) {
 		save_todo(cur, opts);
 		res = do_pick_commit(cur->item, opts);
-		if (res) {
-			if (!cur->next)
-				/*
-				 * An error was encountered while
-				 * picking the last commit; the
-				 * sequencer state is useless now --
-				 * the user simply needs to resolve
-				 * the conflict and commit
-				 */
-				remove_sequencer_state(0);
+		if (res)
 			return res;
-		}
 	}
 
 	/*

t/t3510-cherry-pick-sequence.sh

@@ -203,10 +203,10 @@ test_expect_success '--abort refuses to clobber unrelated change, harder case' '
 	test_cmp_rev initial HEAD
 '
 
-test_expect_success 'cherry-pick cleans up sequencer state when one commit is left' '
+test_expect_success 'cherry-pick still writes sequencer state when one commit is left' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..picked &&
-	test_path_is_missing .git/sequencer &&
+	test_path_is_dir .git/sequencer &&
 	echo "resolved" >foo &&
 	git add foo &&
 	git commit &&
@@ -227,7 +227,7 @@ test_expect_success 'cherry-pick cleans up sequencer state when one commit is le
 	test_cmp expect actual
 '
 
-test_expect_failure '--abort after last commit in sequence' '
+test_expect_success '--abort after last commit in sequence' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..picked &&
 	git cherry-pick --abort &&