[XML-SIG] addition of "encoding='iso8859-1'" in xml prolog

[Dieter Maurer]

The XML generators in our XML package (0.5.1) do not
generate UTF-8, but use the character set that happens to
be Pythons character set.

I think, we should allow for an encoding hook
and include a corresponding "encoding" declaration
in the XML prolog.

Tim Lavoie used XBEL (ns_parse.py) on bookmarks with
international (iso8859-1) entries. The resulting
XML was not parsable, because some of the non-ASCII
characters led to invalid UTF-8 codes.

- Dieter