[AC pkgs (prog-modes)] diff-mode regexp fixes, fix faces for 21.4

This makes diff-mode.el recognize hunk and file boundaries better and makes faces work as intended on 21.4 which doesn't have the :inherit specifier. Will commit tomorrow unless someone yells. 2005-12-01 Ville Skyttä <scop(a)xemacs.org&gt; * diff-mode.el: Sync hunk and file recognition improvements and some trivial bits from GNU Emacs CVS. (diff-removed-face): Don't use :inherit (not in 21.4). (diff-added-face): Ditto. (diff-function-face): Ditto. (diff-nonexistent-face): Ditto.