longer comes from the project directory (really, my source directory
in the various projects). Instead, the source code comes from one of
two places:

* Using fetch on the inner ops and boss, make a special request to the
  outer webserver to return a tarball, currently stored in
  /usr/testbed/src, and created by toplevel makefile target "elabinelab".
  So, in your object tree (preferably one that is pure, without any of your
  own hacks) run "make elabinelab" and it will create the tarfile for you.
  The tarball is returned only to elabinelab experiments providing the
  experiment secret key (a variant of the existing spewrpmtar file stuff).

* Using the standard tarfile install command, albiet indrectly cause of how
  we hide all of the elabinelab NS goo. So, in your NS file you can do:

	tb-elab-in-elab 1
	set ::TBCOMPAT::elabinelab_source_tarfile \
			"/proj/testbed/tarfiles/emulab-src.tar.gz"

  Which will arrange for this tarfile to be installed in /usr/src, and then
  copied to the approriate place later when inner boss and inner ops are
  setup. The tarfile should be created in the top of your testbed source
  tree. This is given preference over method 1 above.

XXX Currently the tarfile is unpacked in /usr/src cause install-tarfile
does not create the target directory. As soon as we have new images, I'll
move this unpacking to a more suitable place.