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.
adding dir/bar
adding foo
dir/bar
foo
committed changeset 0:d44511117907
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
committed changeset 1:a85812e0561a
adding a
adding c
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)