Merge branch 'lp/diffstat-with-graph'

"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 (2)
* lp/diffstat-with-graph:
t4052: work around shells unable to set COLUMNS to 1
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