..
    ;; 2015-09-15T22:15:14+0200 mirko.luedde@gmail.com: GREP_OPTIONS
    ;; is deprecated since grep version 2.20. Using it provides
    ;; annoying warning messages. Please fix!
    ;; (setenv "GREP_OPTIONS"
    ;;    (concat (getenv "GREP_OPTIONS")
    ;;    " --color=" (if (eq grep-highlight-matches 'always)
    ;;    "always" "auto")))
..

Thanks a lot, Mirko