Golang: logclient does not check signature of STH

[dndx]

Currently the Golang logclient does not check the the signature returned by the /ct/v1/get-sth as defined in RFC 6962 section 4.3.

Seems that there is already a function SignatureVerifier.VerifySTHSignature() in signatures.go that can be used to check the signature of a STH, just need to integrate it with logclient to actually check the sig.

Related to this, getConsistencyProofResponse, getAuditProofResponse and getEntryAndProofResponse should probably be checking against STH for integrity as well.

[rolandshoemaker]

Fixed by #1316.