There are lots of features added - too much to list here.
Still compatible enough to work with products and user data written for
zope-2.5, so we can stay in the zope25 directory for now.
extension Makefile fragments, because they really don't have anything to
do with the buildlink[12] frameworks. Change all the Makefiles that use
application.buildlink.mk and extension.buildlink.mk to use application.mk
and extension.mk instead.