Log Message:
py-libxslt was not actually depending on python.
Juggle the includes to fix that.

Because py-libxml2's bl3 file includes pyversion.mk, py-libxslt must
include pyversion.mk itself first; otherwise, because pyversion.mk can
only be applied once, the python dependence ends up in the wrong place
in the buildlink tree.

PKGREVISION -> 1.