Give the hunk comment its own color

Inspired by the coloring of quilt.

Introduce a separate color and paint the hunk comment part, i.e. the name
of the function, in a separate color "diff.func" (defaults to plain).

Whitespace between hunk header and hunk comment is printed in plain color.

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.h

@@ -130,6 +130,7 @@ enum color_diff {
 	DIFF_FILE_NEW = 5,
 	DIFF_COMMIT = 6,
 	DIFF_WHITESPACE = 7,
+	DIFF_FUNCINFO = 8,
 };
 const char *diff_get_color(int diff_use_color, enum color_diff ix);
 #define diff_get_color_opt(o, ix) \