[xmlsec] Microsoft .NET compatibility

[Jesse Pelton]

I'm converting from .Net's DSig implementation to XMLSec. I have had zero
interoperability problems. (Note that my requirements are pretty simple.)
Signatures generated by either one can be validated by the other. As near as
I can tell, both are correct implementations (at least correct enough for my
purposes), and interoperable.

I can't speak to encryption or WS-security, as I don't use them.