PR java/21436: imported type name for superclass, with multifile compilation

[Paolo Bonzini]

>Interesting. The GNU Classpath upstream version has this:
>
>public abstract class X509Certificate
>  extends java.security.cert.Certificate  // XXX workaround for gcj bug #17845
>  implements X509Extension
>  
>
It looks like PR 21436 indeed.  I've reopened bug #17845 and assigned it 
to me.

Paolo