this resolves many security issues, as well as removing a ton of boilerplate code.
It may be desirable to react to permission denied; this can be done by overriding Command->testPermission(), or by using setPermissionMessage() to set a custom permission denied message.
this stuff has different functionality than everything else in the
command namespace (specifically console handling), so it doesn't belong
in here.
I know that this will probably break some plugins, but I don't care,
because plugins shouldn't have been abusing ConsoleCommandSender in the
first place.
