The PDF visualizer http://issuu.com/ISSUU is a popular service
which shows PDF documents "a page a time". Due to the way it is
implemented, internal links in these documents are not allowed.
Instead, they must be converted to external ones in the form
http://issuu.com/action/page?page=PAGENUMBER. The package
patches hyperref to produce external links in the required form
instead of internal links created by \ref, \cite and other
commands. Since the package redefines the internals of
hyperref, it must be loaded it AFTER hyperref.
