Turn SSH-1 ciphers into a classoid.

The interchangeable system of SSH-1 ciphers previously followed the
same pattern as the backends and the public-key algorithms, in that
all the clients would maintain two separate pointers, one to the
vtable and the other to the individual instance / context. Now I've
merged them, just as I did with those other two, so that you only cart
around a single pointer, which has a vtable pointer inside it and a
type distinguishing it from an instance of any of the other
interchangeable sets of algorithms.

sshbpp.h

@@ -32,7 +32,7 @@ struct BinaryPacketProtocol {
 
 BinaryPacketProtocol *ssh1_bpp_new(void);
 void ssh1_bpp_new_cipher(BinaryPacketProtocol *bpp,
-                         const struct ssh_cipher *cipher,
+                         const struct ssh1_cipheralg *cipher,
                          const void *session_key);
 void ssh1_bpp_start_compression(BinaryPacketProtocol *bpp);