sudo: allow wheel to use chdir
    
    the wheel group already has access to run all commands as root, and with
    that to enter arbitrary directories - for commands which need to be
    executed in a certain directory (for example rails console), avoid the
    need to cd/pushd before calling sudo (which is an annoying step plus
    a cause for administrators to unnecessarily enter an interactive root
    shell if they do not have read access to the target directory) by
    allowing them to use the -D/--chdir option with sudo.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>