rev-list --boundary: show boundary commits even when limited otherwise.

The boundary commits are shown for UI like gitk to draw them as
soon as topo-order sorting allows, and should not be omitted by
get_revision() filtering logic.  As long as their immediate
child commits are shown, we should not filter them out.

Signed-off-by: Junio C Hamano <junkio@cox.net>

revision.h

@@ -7,7 +7,8 @@
 #define SHOWN		(1u<<3)
 #define TMP_MARK	(1u<<4) /* for isolated cases; clean after use */
 #define BOUNDARY	(1u<<5)
-#define ADDED		(1u<<6)	/* Parents already parsed and added? */
+#define BOUNDARY_SHOW	(1u<<6)
+#define ADDED		(1u<<7)	/* Parents already parsed and added? */
 
 struct rev_info;