Merged back the new charm release
Remove symlink before re-creating it.
Remove the revision file.
Remove symlink before re-creating it.

Remove the release symlink to the target directory
served by the GUI server vefore (re)creating it.

This should solve spurious errors while trying to
force the removal of a pre-existing target link.

Also remove the no longer required revision file
(and added it to bzrignore). The file generated
a conflict in the last prodstack deployment.

R=rharding
CC=
https://codereview.appspot.com/147360043
Merged changes from the released charm.
Updated to the newest juju-gui release.
New charm release.