Merge branch 'tb/diffstat-with-utf8-strwidth'

Merge branch 'tb/diffstat-with-utf8-strwidth'

"git diff --stat" etc. were invented back when everything was ASCII
and strlen() was a way to measure the display width of a string;
adjust them to compute the display width assuming UTF-8 pathnames.

* tb/diffstat-with-utf8-strwidth:
  diff: leave NEEDWORK notes in show_stats() function
  diff.c: use utf8_strwidth() to count display width