Revved genx

Just promoted beta4, see 
http://www.tbray.org/ongoing/When/200x/2004/02/20/GenxStatus - major 
refactoring so I could use ERH's c14n conformance suite as test data, 
with the help of Tolpin's XG (expat-genx glue).  I think it's nearly 
finished.  Now that I understand how hard it is to get C14n right while 
being efficient, I feel I ought to bang the Genx drum a bit and 
encourage people to use it.  Thanks to all who helped. -Tim