Merge branch 'lp/diffstat-with-graph' into maint

"log --graph" was not very friendly with "--stat" option and its output
had line breaks at wrong places.

By Lucian Poston (5) and Zbigniew Jędrzejewski-Szmek (3)
* lp/diffstat-with-graph:
  t4052: work around shells unable to set COLUMNS to 1
  test-lib: skip test with COLUMNS=1 under mksh
  Prevent graph_width of stat width from falling below min
  t4052: Test diff-stat output with minimum columns
  t4052: Adjust --graph --stat output for prefixes
  Adjust stat width calculations to take --graph output into account
  Add output_prefix_length to diff_options
  t4052: test --stat output with --graph

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge