set realloc tag in smalloc

Reference: /n/atom/patch/applied2013/smalloctag
Date: Thu Jun 13 05:02:29 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/alloc.c	Thu Jun 13 05:02:17 2013
+++ /sys/src/9/port/alloc.c	Thu Jun 13 05:02:17 2013
@@ -179,6 +179,7 @@
 	if(Npadlong){
 		v = (ulong*)v+Npadlong;
 		setmalloctag(v, getcallerpc(&size));
+		setrealloctag(v, 0);
 	}
 	memset(v, 0, size);
 	return v;