diff: Support 256 colors
diff: Support 256 colors

Add support for more than 8 colors.  Colors can be specified as numbers
-1..255.  -1 is same as "normal".

Signed-off-by: Timo Hirvonen <09e171b3033c470527a0ef359ae4762eec3bf43a@gmail.com>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git