go.crypto/ocsp: allow cert-less responses and support making requests.

Some OCSP responses (notably COMODO's) don't use an intermediate
certificate to sign OCSP responses so this change allowed that.

Additionally, a CreateRequest function is added for creating OCSP
requests.

This change makes one API change: SerialNumber becomes a *big.Int to
match crypto/x509. The original code dates to before encoding/asn1
could cope with big.Ints and using a []byte was a workaround for that.

R=golang-dev
CC=golang-dev
https://golang.org/cl/10402043
2 files changed