revlist.c: introduce --left/right-only for unsymmetric picking

The existing "--cherry-pick" does not work with unsymmetric ranges
(A..B) for obvious reasons.

Introduce "--left-only" and "--right-only" which limit the output to
commits on the respective sides of a symmetric range (i.e. only "<"
resp. ">" commits as per "--left-right").

This is especially useful for things like

    git log --cherry-pick --right-only @{u}...

which is much more flexible (and descriptive) than

    git cherry @{u} | sed -ne 's/^+ //p'

and potentially more useful than

    git log --cherry-pick @{u}...

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -733,6 +733,23 @@ static struct commit_list *collect_bottom_commits(struct commit_list *list)
 	return bottom;
 }
 
+/* Assumes either left_only or right_only is set */
+static void limit_left_right(struct commit_list *list, struct rev_info *revs)
+{
+	struct commit_list *p;
+
+	for (p = list; p; p = p->next) {
+		struct commit *commit = p->item;
+
+		if (revs->right_only) {
+			if (commit->object.flags & SYMMETRIC_LEFT)
+				commit->object.flags |= SHOWN;
+		} else	/* revs->left_only is set */
+			if (!(commit->object.flags & SYMMETRIC_LEFT))
+				commit->object.flags |= SHOWN;
+	}
+}
+
 static int limit_list(struct rev_info *revs)
 {
 	int slop = SLOP;
@@ -788,6 +805,9 @@ static int limit_list(struct rev_info *revs)
 	if (revs->cherry_pick)
 		cherry_pick_list(newlist, revs);
 
+	if (revs->left_only || revs->right_only)
+		limit_left_right(newlist, revs);
+
 	if (bottom) {
 		limit_to_ancestry(bottom, newlist);
 		free_commit_list(bottom);
@@ -1263,6 +1283,10 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->boundary = 1;
 	} else if (!strcmp(arg, "--left-right")) {
 		revs->left_right = 1;
+	} else if (!strcmp(arg, "--left-only")) {
+		revs->left_only = 1;
+	} else if (!strcmp(arg, "--right-only")) {
+		revs->right_only = 1;
 	} else if (!strcmp(arg, "--count")) {
 		revs->count = 1;
 	} else if (!strcmp(arg, "--cherry-pick")) {

revision.h

@@ -59,6 +59,8 @@ struct rev_info {
 			boundary:2,
 			count:1,
 			left_right:1,
+			left_only:1,
+			right_only:1,
 			rewrite_parents:1,
 			print_parents:1,
 			show_source:1,