fix weave arg count check
move the most important check first
we only need the bridge address when launching weave
remove unused var
make 'weave <unknown_command>' a no-op
unbreak script
I have no idea why this matters
(slightly) faster pmtu discovery

Issues with the previous scheme...

When we have just encountered an EMSGSIZE, the odds of encountering
another one straight away, when attemtping to send a verification
packet with the lower mtu, are slim, since for a new, lower mtu to be
set some packet must have made it further then the one that triggered
the icmp3.4 that gave rise to the EMSGSIZE, and we must have received
the resulting icmp3.4. All of which takes time.

Also, sending a bunch of udp packets in rapid succession is not a
great way to improve their chances of making it through to the other
peer, since they could easily all get dropped by a single congestion
event or other network glitch.

Now we send a single verification packet, wait for a short while, and
if we don't get a response then we send another one, wait for longer
period (2x), etc, until some upper bound is reached, at which point we
lower the pmtu and start the verification process again (same as
currently happens).

We are now also calling flush() to send the verification packet, just
as we do for ordinary packets. This makes for shorter code, consistent
error handling, and introduces a nice little recursion :)
switch to ubuntu image for examples
It comes with more stuff pre-installed, such as 'nc', so makes
experimentation just a little more convenient.
link to architecture documentation
document external service access
cosmetic
cosmetic
set up masquerading as part of 'weave launch'
thus simplifying external access
introduce 'weave expose'
which simplifies access to containers from the host, as well as
external access.
fix link
more link fixing
yet more link fixing
correct ports in example
switch tcp nc service for bulk of examples
since udp nc is full of weirdness
deal with pmtu verification confirmation in forwarder goroutine
...rather than connection goroutine.
This is a precurser to smarter pmtu verification, the logic for which
is in the forwarder.
issue #15