Testsuite: Added some tests of client certificates.
Testsuite [SSL]: Use same DN for the RSA certs as for the others.

The RSA cert is created via a different taste of the
Standards.PKCS.Certificate.build_distinguished_name() than
the DSA and ECDSA certs. Reorder the fields to make sure
that the exact same DN is generated in both cases.

Fixes issue where SSL.Context()->find_cert_issuer() either
didn't find the RSA certs, or didn't found only the RSA certs.
Testsuite [SSL]: Fixed some erroneous failures.

The server_ctx list of suites needs to be restored after the Suite-B tests.
Otherwise the server will select a different suite than the testsuite expects.
SSL.ClientConnection: Send client certificate verify packet.

Update certificate_verify_packet() and reenable the related code.

Also fixes several FIXME's regarding the dual use of the
certificate_state variable. It is now strictly used only
for the server certificates.

Client-side support for client certificates should now work.
SSL.ServerConnection: Extract the public key from the client cert.

This is needed to be able to validate the certificate verify message.
SSL.ServerConnection: Fixed NULL-deref.

There's no key exchange in progress at STATE_wait_for_verify time.