[xml] Windows binaries

[Igor Zlatkovic <igor zlatkovic com>]

Hi there,

as of version 2.5.7, libxml2 binary packages for Windows are distributed
with thread-support enabled. This means that this version is not
binary-compatible to the previous versions.

When upgrading, please upgrade all packages you use which depend on libxml2,
means libxslt and xmlsec. Older libxslt and libxmlsec will not work with
threaded libxml2.

If you have your own programs which are linked to the binary libxml*
packages, you will have to recompile them.

Please feed me back about how wise this is and about any problems. If it
doesn't work for everybody, we'll switch back to threadless distribution.

Ciao,
Igor