diff: add --stat for diffstat output
diff/qdiff --stat invokes patch.diffstat() on the diff output.
When in interactive mode, the output's maximum width is determined by the
terminal's width.
% Without -v
access log created - .hg/hgrc respected
% errors
% With -v
listening at http://localhost/ (bound to 127.0.0.1)
% errors
% With --prefix foo
listening at http://localhost/foo/ (bound to 127.0.0.1)
% errors
% With --prefix /foo
listening at http://localhost/foo/ (bound to 127.0.0.1)
% errors
% With --prefix foo/
listening at http://localhost/foo/ (bound to 127.0.0.1)
% errors
% With --prefix /foo/
listening at http://localhost/foo/ (bound to 127.0.0.1)
% errors