Currently, the Account.ChangingPresence property can sometimes spuriously become True. I noticed this when I added it to the output of `mc-tool show` and ran it against an account I never enable (but whose RequestedPresence is 'available' for some reason).

Here's a branch that adds that stuff to mc-tool, fixes this bug, and adds a test. So now the output from mc-tool show looks like this:

     Account: gabble/jabber/will_2ethompson_40collabora_2eco_2euk0
Display Name: Collabora (will.thompson@collabora.co.uk)
  Normalized: will.thompson@collabora.co.uk
     Enabled: enabled
        Icon: im-jabber
    Connects: only when requested
    Nickname: wjt
     Service: Collabora

Presences:
   Automatic: available (2) ""
     Current: available (2) ""
   Requested: available (2) ""
    Changing: no

        (bool) require-encryption = true
      (string) account = will.thompson@collabora.co.uk