nbsp (0xa0) is not a unicode control character, so don't force binary output.

Reference: /n/sources/patch/maybe/diff-nbsp
Date: Thu Dec  5 13:42:54 CET 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/diff/diffio.c	Thu Dec  5 13:42:34 2013
+++ /sys/src/cmd/diff/diffio.c	Thu Dec  5 13:42:33 2013
@@ -138,7 +138,7 @@
 			 * brave new UNICODE world
 			 */
 			cp += chartorune(&r, cp);
-			if (r == 0 || (r > 0x7f && r <= 0xa0)) {
+			if (r == 0 || (r > 0x7f && r < 0xa0)) {
 				binary++;
 				return bp;
 			}