[xmlsec] Undefined with fresh checkout

[Wouter]

Hi,

The current cvs tree gives me the following:

Undefined nn in function xmlSecBnAdd in bn.c

After fixing that, everything (build and test) goes without problems for
xmlsec with mscrypto, except for 
verify  ./tests/merlin-xmldsig-twenty-three/signature-x509-is.xml, but
that's probably because my undefined fix wasn't right. 

Wouter