That file (or a version of it) is also available on any FreeBSD installation as /usr/share/examples/etc/wpa_supplicant.conf.
To me Schmerzmittel's wpa_supplicant.conf file looks fine. It'd be more interesting to see ifconfig output and maybe see if ifconfig wlan0 scan produces any output. Or if there are any error messages in dmesg for ral0.
Thanks for having the courtesy to let us know. Judging from the screenshot, it does seem that it would be possible to get it to work (no guarantee of course) so if you decided to try again, post again.