Load plugins after parsing arguments and potentially printing the

version.  That way, an error loading or initializing a plugin doesn't
break "sudo -h" or "sudo -V".

src/sudo_plugin_int.h

@@ -78,7 +78,7 @@ int sudo_conversation(int num_msgs, const struct sudo_conv_message msgs[],
     struct sudo_conv_reply replies[]);
 int _sudo_printf(int msg_type, const char *fmt, ...);
 
-void sudo_load_plugins(const char *conf_file,
+int sudo_load_plugins(const char *conf_file,
     struct plugin_container *policy_plugin,
     struct plugin_container_list *io_plugins);