XML parser doesn't report multiple top-level elements error

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2103

Reported by Jonas Wallden jonasw@roxen.com

lister:7.2 $ ./bin/pike
Pike v7.2 release 164 running Hilfe v2.0 (Incremental Pike Frontend)
> Parser.XML.Simple()->parse("<a/><b/>", lambda(mixed ...args) { if
(args[0] == "error") werror("err: %O\n", args[3]); return 0; });
Result: ({ })
>

This ought to produce the message "All data must be inside tags".

(See production [1] in http://www.w3.org/TR/REC-xml#sec-well-formed.)