http: include DEL in the test for unprintable chars
http: include DEL in the test for unprintable chars

R=adg, rsc
CC=golang-dev
http://codereview.appspot.com/3631041

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go