Fix various Emacs 24.3 issues.

Here's a patch that fixes several issues that appeared when I switched to Emacs 24.3:

1. diff-mode faces require explicitly setting background to nil.  This is necessary because the default values set the background to a specific color, which of course is not compatible with zenburn.  I also added a simple tweak for the diff-refine-* faces.

2. New compilation-mode-line faces need to be set to zenburn-compatible values.

3. The success and warning faces need to be set to zenburn-compatible values.