Add runtime dependency on ed
    
    Use of 'patch --ed' requires ed. For those unfamiliar with this
    functionality (like me), here is a reproducer:
    $ echo foo > a
    $ cp a b
    $ echo bar >> b
    $ diff --ed a b > patch
    $ patch --ed a patch
    patch: /usr/bin/ed subprocess failed: No such file or directory
    patch: **** /usr/bin/ed FAILED
    
    I ran into this issue when running 'quilt annotate'.