[XML-SIG] gray areas in Python SAX API

[Lars Marius Garshol]

* Alexandre Fayolle
|
|  * PyExpat uses '', xmlproc uses None. Using None has a strong
|    impact on code using DOM.

As far as I can see, expatreader revision 1.15 is already fixed. So
apparently nothing needs to be done about this.

--Lars M.