All commands should work now.

There is probably a better way of doing this, but currently
parseCustomFile can modify globals (e.g. TOPOS) as well as
instance variables (self.validate) and classes (e.g. MyTopo),
which are also in the global name space.

Inconveniently enough, lambdas don't seem to be full closures
in Python; if they were, this trickiness would be unnecessary.

Even so, using execfile() seems like it might be a bit dubious...

This increases flexibility by allowing a topology to be manually created
in Python, or specified using another format, without having to create
a Topo object first.

However, Topos are useful, and are still the default topology object!

NOX Install is covered in the wiki and in util/deb/install_nox.sh.

Shell now works (although we should use quietRun instead to avoid
file descriptor problem!)

exit/quit/EOF now all exit.

Renamed pingall and pingpair to make them easier to type - I think
commands should not require use of the shift key in general, although
ping-all and ping-pair might be OK.

Simplifies installation step

Defining custom topologies, switch types, controllers, and hosts is now
much easier.  Plus, all Ripcord-specific stuff has been moved out.

Convert CLI to use Python Cmd object, which provides line editing.

with the exception of topo.py, which I haven't touched.

- some namespace conflicts due to unpep8
- fixed infinite recursion caused by removing redundant makeIntfPair