Merge branch 'js/add-i-color-fix'

Merge branch 'js/add-i-color-fix'

"git add -i" failed to honor custom colors configured to show
patches, which has been corrected.

* js/add-i-color-fix:
  add -i: verify in the tests that colors can be overridden
  add -p: prefer color.diff.context over color.diff.plain
  add -i (Perl version): color header to match the C version
  add -i (built-in): use the same indentation as the Perl version
  add -p (built-in): do not color the progress indicator separately
  add -i (built-in): use correct names to load color.diff.* config
  add -i (built-in): prevent the `reset` "color" from being configured
  add -i: use `reset_color` consistently
  add -p (built-in): imitate `xdl_format_hunk_hdr()` generating hunk headers
  add -i (built-in): send error messages to stderr
  add -i (built-in): do show an error message for incorrect inputs