crypto/x509: allow ECDSA public keys to be marshaled.
crypto/x509: allow ECDSA public keys to be marshaled.

The public key serialization from CreateCertificate is factored out to be
used in MarshalPKIXPublicKey.
Testcode with one P224 ECDSA keypair has been added.

R=golang-dev, agl
CC=agl, golang-dev
https://codereview.appspot.com/13427044

Committer: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,apparentlymart/golang,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go