Clean up TLSv1.2 certificate request handshake data.

Clean up TLSv1.2 certificate request handshake data.

Currently cert_req is used by clients and cert_request is used by servers.
Replace this by a single cert_request used by either client or server.
Remove the certificate types as they are currently unused. This also fixes
a bug whereby if the number of certificate types exceeds SSL3_CT_NUMBER
the number of bytes read in is insufficient, which will break decoding.

ok inoguchi@ tb@