<= on functions doesn't behave as expected.

Imported from https://youtrack.roxen.com/issue/PIKE-124

Reported by @grubba

Pike v8.0 release 622 running Hilfe 3.5 (Incremental Pike Frontend)
> Parser.XML.Tree.AttributeNode <= Parser.XML.Tree.Node;
(1) Result: 1
> ((program)Parser.XML.Tree.AttributeNode) <= ((program)Parser.XML.Tree.Node);
(2) Result: 0