Note: we should probably rename it "setup()" to avoid confusion.

Also trying to fix NOX cmdline opt, but broken at the moment.

Controllers are no longer namespace-able, and all calls need one fewer
arg.

Also use more sensible temporary variable name.

We should check NOXController and RemoteController to make sure that
they are not broken, but I cannot do this at the moment.

Also switch from print to info statements, to enable a non-verbose
clean.  Instead of 'mnclean', now run 'mn -c'.

Now you can pass a topology name followed by params.  For example, to
create a switch with 3 hosts:

  sudo mn --topo single,3

Also print warning if user chooses a loglevel that will hide CLI output.

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!

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