fix magit faces

This doesn't theme magit more completely, it just fixes shortcomings
in what others have already done.
Theme diff-hl
Merge branch 'master' of github.com:bbatsov/zenburn-emacs
Merge pull request #166 from tarsius/fix-magit

fix magit faces
Refine diff-hl's faces
Merge branch 'master' of github.com:bbatsov/zenburn-emacs
Merge remote-tracking branch 'upstream/master'

Conflicts:
	zenburn-theme.el