Tweak diff colors

Tweak diff colors

This patch does:

 - always reset the color _before_ printing out the newline.

   This is actually important. You (and Johannes) didn't see it, because
   it only matters if you set the background, but if you don't do this,
   you get some random and funky behaviour if you pick a color with a
   non-default background (which still potentially has problems with tabs
   etc, but less so).

 - allow people to have a different color for the "file headers"
   (DIFF_METAINFO) and for the "fragment header" (DIFF_FRAGINFO). Also,
   make a difference between "normal color" and "reset colors"

 - default to red/green for old/new lines. That's the norm, I'd think.

 - instead of that eye-popping (and eye-ball-with-a-fondue-fork-popping)
   purple color for metadata, use bold-face for file headers, and cyan for
   the frag headers. I actually prefer the "gray background" for that, but
   it only works well in xterms, so COLOR_CYAN it is..

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>