Reported by John Darrington <john@darrington.wattle.id.au>.
* gnu/packages/guile.scm (guile-ssh): Move to...
* gnu/packages/ssh.scm (guile-ssh): ... here. New variable.
This fixes a circular dependency issue, as reported at
<https://lists.gnu.org/archive/html/guix-devel/2013-12/msg00024.html>.