butch scripts use readlink -f which is not posix

[rofl0r]

... so it may currently not be used on Mac OS X, and maybe some BSDs...

TODO: find portable way to achieve the same

readlink_f() {
readlink "$1" || printf "%s\n" "$1" | sed -e 's,\\,/,g'
}

this possible candidate works for the cases where readlink doesn't return anything, and the program is in $PATH, but not for the case of relative symlinks: e.g.

$ readlink /bin/butch
../opt/sabotage-core/bin/butch

[rofl0r]

hoping that @nero soon completes his https://github.com/nero/realpath.sh ..