Allow paths under Attic directories to be excluded, too.

Pass excluded_paths to _RepositoryWalker._generate_attic_cvs_files()
and teach that method to exclude attic files that are listed.

Problem reported by: Etan Reisner <deryni@gmail.com>

git-svn-id: http://cvs2svn.tigris.org/svn/cvs2svn/trunk@5433 be7e6eca-30d4-0310-a8e5-ac0d63af7087