status: show commit sha1 in "You are currently cherry-picking" message

Especially helpful when cherry-picking multiple commits.

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Acked-by: Matthieu Moy <Matthieu.Moy@grenoble-inp.fr>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

wt-status.h

@@ -88,6 +88,7 @@ struct wt_status_state {
 	char *detached_from;
 	unsigned char detached_sha1[20];
 	unsigned char revert_head_sha1[20];
+	unsigned char cherry_pick_head_sha1[20];
 };
 
 void wt_status_prepare(struct wt_status *s);