It assumed addresses were unused if node_id was NULL.  This used to be
true before the introduction of per-experiment dynamic address pools (when
public addresses were mapped one-to-one with VMs).  Unfortunately this
code was not updated when experiment address pools were added, and so
it would have permitted the deletion of currently assigned addresses.

This commit is intended to makes the license status of Emulab and
ProtoGENI source files more clear.  It replaces license symbols like
"EMULAB-COPYRIGHT" and "GENIPUBLIC-COPYRIGHT" with {{{ }}}-delimited
blocks that contain actual license statements.

This change was driven by the fact that today, most people acquire and
track Emulab and ProtoGENI sources via git.

Before the Emulab source code was kept in git, the Flux Research Group
at the University of Utah would roll distributions by making tar
files.  As part of that process, the Flux Group would replace the
license symbols in the source files with actual license statements.

When the Flux Group moved to git, people outside of the group started
to see the source files with the "unexpanded" symbols.  This meant
that people acquired source files without actual license statements in
them.  All the relevant files had Utah *copyright* statements in them,
but without the expanded *license* statements, the licensing status of
the source files was unclear.

This commit is intended to clear up that confusion.

Most Utah-copyrighted files in the Emulab source tree are distributed
under the terms of the Affero GNU General Public License, version 3
(AGPLv3).

Most Utah-copyrighted files related to ProtoGENI are distributed under
the terms of the GENI Public License, which is a BSD-like open-source
license.

Some Utah-copyrighted files in the Emulab source tree are distributed
under the terms of the GNU Lesser General Public License, version 2.1
(LGPL).

Now accept a range of addresses from first-last, instead of base+mask.
That way, arbitrary ranges can be speficied (address blocks are no
longer limited to aligned powers of two).

Documentation to follow.