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.

diffstat: print 0 instead of nothing for 0 adds or removes This is in line with how the stock diffstat behaves when processing a single diff with no line modifications (like a binary diff).

update tcsh_completion for the new forget and summary commands