[xslt] header taint issues

["Vakoc, Mark" <Mark_Vakoc jdedwards com>]

Ok, I pulled down the latest libx* after being about 6 months behind in
releases.  I had to fix a couple of issues with the new header taint
system (which I like much better than any .def.src solution, as this
actually seems to work!).

Diff1:  Basicly I added extern to the XMLPUBVAR definitions (needed for
const variables) and one function used XMLPUBVAR instead of XMLPUBFUN
(or vice versa, can't remember).

Diff2:  Same thing with the extern for libxslt/libexslt.

diff1.diff

diff2.diff