(diff-file-header): Change foreground color from

(diff-file-header): Change foreground color from
yellow to green on light backgrounds.
(diff-context): Inherit from `shadow' only for color/grayscale
with more than 88 colors.
(diff-indicator-removed, diff-indicator-added)
(diff-indicator-changed): New faces.
(diff-font-lock-keywords): Use new faces.  Regroup rules.
Add "^---$" for `normal' diff format.  Fontify `#' lines with
font-lock-comment-delimiter-face and font-lock-comment-face.
Add `#' to ^[^...] in the rule for `diff-context-face'.