using make to generate cowfortune file

this will allow to set some path specific configuration
for the cowsay and fortune commands especially for root
where /usr/games does not belong to the path because
of safe_path
enforce 0644 mode for config files on installation
dont run Makefile cowfortune target on install

this avoids problems if someone uses sudo to install
and the PATH is not properly set up, but uses a
user tty with proper PATH to generate the cowfortune
script.