first cut at documenting the change to malloc doing a partial 'junk' by

default and the new 'j' option to disable this; ok jmc@

src/lib/libc/stdlib/malloc.3

@@ -30,9 +30,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: malloc.3,v 1.76 2014/04/22 15:02:16 jmc Exp $
+.\"	$OpenBSD: malloc.3,v 1.77 2014/04/30 23:28:05 sthen Exp $
 .\"
-.Dd $Mdocdate: April 22 2014 $
+.Dd $Mdocdate: April 30 2014 $
 .Dt MALLOC 3
 .Os
 .Sh NAME
@@ -271,6 +271,11 @@ Currently junk is bytes of 0xd0 when allocating; this is pronounced
 .Dq Duh .
 \&:-)
 Freed chunks are filled with 0xdf.
+.It Cm j
+.Dq Don't Junk .
+By default, small chunks are always junked, and the first part of pages
+is junked after free.
+This flag disables the default so that no junking is performed.
 .It Cm P
 .Dq Move allocations within a page.
 Allocations larger than half a page but smaller than a page