Merge branch 'ap/maint-diff-rename-avoid-overlap'

The logic used by "git diff -M --stat" to shorten the names of
files before and after a rename did not work correctly when the
common prefix and suffix between the two filenames overlapped.

* ap/maint-diff-rename-avoid-overlap:
  tests: make sure rename pretty print works
  diff: prevent pprint_rename from underrunning input
  diff: Fix rename pretty-print when suffix and prefix overlap

diff --cc diff.c
Simple merge