Support juju-gui-source=branch:revno

config.yaml

 options:
   juju-gui-source:
     description: |
       Where to install Juju GUI from. Possible values are:
       - 'stable' (default): the latest stable release will be deployed;
       - 'trunk': the latest trunk release will be deployed;
       - a stable version (e.g '0.1.0'): the specified stable version will be
         deployed;
       - a trunk version (e.g '0.1.0+build.1'): the specified trunk version
         will be deployed;
       - a Bazaar branch (e.g. 'lp:juju-gui'): a release will be created and
         deployed from the specified Bazaar branch. 'http://' prefixed branches
-        work as well.
+        work as well. It is also possible to include the specific branch
+        revision, e.g. 'lp:juju-gui:42' will checkout revno 42.
       - a 'url:' prefixed url (ex: url:http://...) of a specific location
         to pull a release from.
     type: string
     default: stable
   juju-api-branch:
     description: |
       The Juju API Bazaar branch (implementing the WebSocket server).
       Since juju-core includes the WebSocket API server out of the box, this
       option is ignored if the charm is deployed using juju-core.
     type: string
@@ skipping 87 matching lines @@
       the GUI needs.  This will be made more explicit soon.  For now, look in
       the source: hooks/install and hooks/backend.py in particular.
     type: boolean
     default: true
   charmworld-url:
     description: |
       The URL of the charm catalog site ("charmworld") from which charm catalog
       data will be drawn.
     type: string
     default: https://manage.jujucharms.com