
add_dig_exit
Adds an exit you have to uncover
Needs more doc's bug Piper.

add_dig_exit(string direc, mixed dest);
i.e.
add_dig_exit("down",({"hole","pathtonextroom"});

Once you've dug enough, a "hole" will appear, leading
to pathtonextroom

(Wonders why this isn't a modify exit)
