crypto/x509: fix build
crypto/x509: fix build

This pulls in changes that should have been in 3faf9d0c10c0, but
weren't because x509.go was part of another changelist.

TBR=bradfitzgo

R=bradfitzgo
CC=golang-dev
http://codereview.appspot.com/4433056

apparentlymart/golang,gnanderson/go,apparentlymart/golang,ssrl/go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,dsriram/golang,ssrl/go,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,gnanderson/go,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,ssrl/go,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,ssrl/go,tv42/old-go,tv42/old-go,apparentlymart/golang,gnanderson/go,tv42/old-go,dsriram/golang,dsriram/golang,ssrl/go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,ssrl/go,ssrl/go,dsriram/golang,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,tv42/old-go