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.h

@@ -152,6 +152,7 @@ struct diff_options {
 	diff_format_fn_t format_callback;
 	void *format_callback_data;
 	diff_prefix_fn_t output_prefix;
+	int output_prefix_length;
 	void *output_prefix_data;
 };