Merge branch 'jc/ws-error-highlight'

"git diff/log --ws-error-highlight=<kind>" lacked the corresponding
configuration variable to set it by default.

* jc/ws-error-highlight:
diff: introduce diff.wsErrorHighlight option
diff.c: move ws-error-highlight parsing helpers up
diff.c: refactor parse_ws_error_highlight()
t4015: split out the "setup" part of ws-error-highlight test

diff --cc Documentation/diff-config.txt
Simple merge

diff --cc Documentation/diff-options.txt
Simple merge

diff --cc diff.c
index f5d6d7e4f6700d86089ac84e930c7898ae01c6d8,9acf04f5b02b113f11801c8c5d19b6ec5f84cb62..569f615d3b13b2a57bc0f91ac35ae0fd12c52ef0
--- 1/diff.c
--- 2/diff.c
+++ b/diff.c
@@@ -254,8 -263,14 +292,17 @@@ int git_diff_ui_config(const char *var
                return 0;
        }
  
 +      if (git_diff_heuristic_config(var, value, cb) < 0)
 +              return -1;
++
+       if (!strcmp(var, "diff.wserrorhighlight")) {
+               int val = parse_ws_error_highlight(value);
+               if (val < 0)
+                       return -1;
+               ws_error_highlight_default = val;
+               return 0;
+       }
+ 
        if (git_color_config(var, value, cb) < 0)
                return -1;