by casey.marshall:
Need to add a signature verification method to *PublicKey for newly added
*packet.UserAttribute, and a test case per
https://golang.org/cl/13464044/#msg3. (My current user attribute signature
verification is in Hockeypuck but really belongs here)
I'll add it as:
func (pk *PublicKey) VerifyUserAttributeSignature(signingKey *PublicKey, uat
*UserAttribute) { ... }