[sugar] Tubes message dropping

[J.M. Maurer]

To the Tube guys:

Do you drop messages on your XMPP server? An AbiCollab packet that
contains an image never gets sent over, resulting in documents getting
out of sync (in fact, the PS seems to disconnect the buddy altogether
from the Write session).

As AbiCollab assumes packets are never dropped (and are in-order), this
results in issues like http://dev.laptop.org/ticket/2253

What would be the proper way to solve this? I can implement full
checking of message ordering/dropping in AbiCollab ofcourse, but that
seems like a solution at the wrong level.

Cheers,
  Marc