X509 names, like everything else X509, are ludicrously general. This
change keeps the raw version of the subject and issuer around for
matching. Since certificates use a distinguished encoding, comparing
the encoding is the same as comparing the values directly. This came
up recently when parsing the NSS built-in certificates which use the
raw subject and issuer for matching trust records to certificates.

R=bradfitz
CC=golang-dev
https://golang.org/cl/5275047