### Please describe the problem.
When using the git-annex webapp with the --listen paramter it as usual asks one to create a new repository on first startup. Selecting a repository location here and clicking "Make repository" button leads to a never ending loading browser and some git zombies. 

### What steps will reproduce the problem?
Two machines needed

1. On machine one: git-annex webapp --listen=\<machine1-public-ip\>:34561 (you can choose another port as well)
2. On machine two: use a browser to go to the url the last step gave you
3. Click on make repository


### What version of git-annex are you using? On what operating system?
* git-annex version: 4.20130601
* build flags: Assistant Webapp Pairing Testsuite S3 WebDAV Inotify DBus XMPP DNS
* built using cabal
* on Ubuntu 13.04 32bit


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log

[2013-06-12 21:59:37 CEST] main: starting assistant version 4.20130601
WebApp crashed: unable to bind to local socket
[2013-06-12 21:59:37 CEST] WebApp: warning WebApp crashed: unable to bind to local socket

  dbus failed; falling back to mtab polling (ClientError {clientErrorMessage = "runClient: unable to determine DBUS address", clientErrorFatal = True})

  No known network monitor available through dbus; falling back to polling
(scanning...) [2013-06-12 21:59:37 CEST] Watcher: Performing startup scan
(started...) 


# End of transcript or log.
"""]]

> The problem is that, when a port is specified, it is used for each web
> server started, and the process of making a new repository unavoidably
> requires it to start a second web server instance. This would also affect
> switching between existing repositories in the webapp. I don't see
> any way to make it not crash here, except for ignoring the port it was told
> to use when something else is already listening there. --[[Joey]] 

[[!tag /design/assistant]]
