fixes #143

Fixes #94

fixes #161

It appears that under certain conditions, such as when a
namespace exits, both ends of a veth pair may get dumped
into the root namespace. We therefore now remove an interface
both from its home namespace and from the root namespace.

This disables slicing by default but fixes bandwidth limits.
Eventually we want to enable both to work together, but for now
this enables one or the other depending on the dpopts setting.

Currently, slicing on the user switch breaks bandwidth limits.
We don't yet have a good way of using both of them at the same time.
I'm inclined to turn off slicing by default, but I have to think
about it and also see if any one is using it...

Fixes another Graph regression relative to NetworkX.

RipL broke because the NetworkX Graph object that was used previously
for topologies is an undirected graph:

>>> import networkx as nx
>>> g=nx.Graph()
>>> g.add_edge(0,1)
>>> g[1]
{0: {}}
>>> g[0]
{1: {}}

There is a separate DiGraph object in NetworkX for directed behavior.

The minimal replacement previously implemented DiGraph behavior.

>>> from mininet.topo import Graph
>>> g2=Graph()
>>> g2.add_edge(0,1)
>>> g2[0]
[1]
>>> g2[1]
[]

This commit restores undirected graph behavior.

Commit 65c35b65 'Remove networkx dependency' broke this line from RipL:

    nodes = [n for n in self.g[name] if self.layer(n) == layer]

To work around this, RipL code would have to be changed to something
like this:

    nodes = [n for n in self.g.data[name] if self.layer(n) == layer]

...which would use an internal variable, data.

It seems cleaner to add this one little feature from NetworkX Graph objects.

If NBEEURL is defined when running install.sh, use that location.

Enables use of a local mirror for netbee download.

Thanks to David Erickson for the code.

node: Make OVS switches reconnect quickly

fixes #152 hopefully

node: Allow OVSSwitch to run in userspace mode

Ordinarily, OVS switches back off when they can't reach their controllers.
Under the type of scenarios where Mininet is used, I think this is
probably just inconvenient.  This patch set controllers to attempt to
reconnect every second.

This adds a datapath parameter to OVSSwitch which allows one to tell OVS to
run in userspace mode rather than kernel mode.  From the commandline, this
is --switch=ovsk,datapath=user.

Note that this makes "ovsk" and the OVSKernelSwitch alias misnomers.  Since
the default behavior is still kernel mode, this is hopefully harmless.

This is the second version of this patch, which changes the argument name
and values according to Bob's suggestion.

The previous version (12-05-16) does not compile on Ubuntu 12.10.

Also use a local variable to reduce duplication.

fixes #144