Should warn when "bzr branch" is used on a repository root

[Jelmer Vernooij]

 affects bzr-svn

bzr-svn should warn when the user is trying to branch the repository
root if that doesn't match the set or guessed layout, and should instead
suggest the user to use svn-import.

e.g.:
warning: Cloning Subversion repository at %s as branch. To import the
individual branches in the repository, use "bzr svn-import".
--
Jelmer Vernooij <email address hidden> - http://samba.org/~jelmer/
Jabber: <email address hidden>

[Jelmer Vernooij (jelmer)]

 status triaged
 importance low