#16 improved boolean support

[Robert Spier]

1) SOAPpy was emitting xsd::bool instead of
xsd::boolean. (while some servers might accept that...
Axis doesn't.)

2) make the parser a little more flexible with values
returned for xsi:nil and xsi:null -- it's a bool, not
an int.

-R

[Robert Spier]

patch to fix some bool support