[XML-SIG] SAX API clarifications

[Lars Marius Garshol]

* Martin v. Loewis
| 
| Leaving the default at true means that we have to change
| expatreader.  That change may break existing applications which
| don't care to set the feature explicitly.

* Lars Marius Garshol
| 
| Actually, expatreader in CVS is already changed. [...] Since
| nobody's complained about this it seems likely that the problem is
| not going to be very substantial.

Uh, sorry. I misunderstood what Martin was writing, so please
disregard this.

--Lars M.