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* state...

Add global flag.

Derive type list from underlying image.

clone_image is a wrapper around newimageid_ez and create_image, that
simplifies the most common operation; creating a new imageid derived
from the image/os that is currently running in the node, and then
taking a snapshot of the node. So for example, if node pcXXX is
running image FREEBSD, and you want to create a custom image from that
node, all you need to do:

	boss> clone_image myfreebsd pcXXX

which will create the new descriptor, deriving everything from the
FREEBSD image on the node, and then take a snapshot from pcXXX. If
the descriptor already exists, just take the snapshot.

So what if you do:

	boss> clone_image FREEBSD pcXXX

well, the image is always looked up in the project the node is
currently attached to, so in fact a new descriptor is created in that
project, and you do not actually overwrite an image from some other
project. 

I've added some locking to images to prevent concurrent snapshots.
This seemed like a good idea since this script is going to be used
from the ProtoGeni interface. More on this in another commit.