add some "find | xargs chmod"s to the includes target, like were in
   the old include/Makefile, so that installed system headers have
   correct permissions.



hm... this reminds me.  i did a `make build UPDATE=1' last night and
i was somewhat annoyed that the installation of sys header files is
done anyway, because of the usage of pax(1) to do this...


the good parts about this are that we don't need to keep a list of
which headers in src/sys are installed.  but i question that, at
times, too.  everything else we install we keep a list of..


anyone else have comments on what the best thing here is ?