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.
#!/bin/sh
mkdir a
cd a
hg init
echo foo > b
hg add b
hg ci -m "b" -d "1000000 0"
chmod -w .hg/store
cd ..
hg clone a b
chmod +w a/.hg/store # let test clean up
cd b
hg verify