[XeTeX] minor bug within XeLaTeX

[Akira Kakuto]

Hi,

> What is questionable, I suppose, is the use of this string as a  
> default for the PDF Creator field.

xdvipdfmx(dvipdfmx) uses itself as a default PDF Producer
and DVI(XDV) creator as a default PDF Creator.
The function dvi_comment() is used at only one place.
If you admit the comment string as a default creator,
the simplest fix will be to rewrite
    pdf_doc_set_creator(dvi_comment());
in dvipdfmx.c like
    pdf_doc_set_creator(dvi_comment() + 1);

Thanks,
Akira