This is never going to work, so complain about trying to do it to help with
catching this bug.
This is possible thanks to the new OnDynamicBind() method invoked whenever a
dynamic event handler is bound to a control, so this doesn't detect all
possible occurrences of the bug (such as specifying the handler in a static
event table or in a validator), but it's still better than nothing.
In the future OnDynamicBind() should be extended for other invalid calls, e.g.
binding a handler for wxEVT_TEXT_ENTER to a non-text control shouldn't work
neither, ideally.