Incorrect author when saving document in a different wiki.

In api.Document, we have the method saveDocument, which will be called
when saving a document:

    protected void saveDocument(String comment, boolean minorEdit) throws XWikiException
    {
        XWikiDocument doc = getDoc();
        doc.setAuthor(this.context.getUser());
        if (doc.isNew()) {
            doc.setCreator(this.context.getUser());
        }
        getXWikiContext().getWiki().saveDocument(doc, comment, minorEdit, getXWikiContext());
        this.cloned = false;
    }

However, context.getUser() always seems to return a username that is
unqualified with respect to the wikiname. This means that when saving
a document in a different wiki the author will be incorrect.

This bug is a problem when executing scripts from the main wiki to do
various administrative tasks on virtual wikis, for instance to assign
programming rights. (Even though a user with programming rights can
work around it.)

In virtual mode, it doesn't seem possible to assign edit rights on the
main wiki to a user of a virtual wiki via the user interface, so it
seems that this cannot normally be exploited to obtain programming
rights.

A quick fix is to just add in the wiki name:

    DocumentReference ref = doc.getDocumentReference();
    if (!ref.getWikiReference().getName().equals(context.getDatabase())) {
       doc.setAuthor(context.getDatabase() + ":" + context.getUser());
    }

But I'd guess that in the long run, we would like to add a user
reference type and a serializer to the EntityReference family to
represent user names?