Move the registration of callback functions to special functions

designed for that.  This removes the potential error to mix data and
function pointers.

Please note that I'm a little unsure how incorrect calls to the old
ctrl functions should be handled, in som cases.  I currently return 0
and that's it, but it may be more correct to generate a genuine error
in those cases.

ssl/s2_lib.c

@@ -230,6 +230,9 @@ static SSL_METHOD SSLv2_data= {
 	ssl_bad_method,
 	ssl2_default_timeout,
 	&ssl3_undef_enc_method,
+	ssl_undefined_function,
+	ssl2_callback_ctrl,	/* local */
+	ssl2_ctx_callback_ctrl,	/* local */
 	};
 
 static long ssl2_default_timeout(void)
@@ -335,11 +338,21 @@ long ssl2_ctrl(SSL *s, int cmd, long larg, char *parg)
 	return(ret);
 	}
 
+long ssl2_callback_ctrl(SSL *s, int cmd, void (*fp)())
+	{
+	return(0);
+	}
+
 long ssl2_ctx_ctrl(SSL_CTX *ctx, int cmd, long larg, char *parg)
 	{
 	return(0);
 	}
 
+long ssl2_ctx_callback_ctrl(SSL_CTX *ctx, int cmd, void (*fp)())
+	{
+	return(0);
+	}
+
 /* This function needs to check if the ciphers required are actually
  * available */
 SSL_CIPHER *ssl2_get_cipher_by_char(const unsigned char *p)