For maps like NIS's services map, we need to be able to construct entries that look like this:
"telnet/tcp" -> "telnet 23/tcp"[[BR]]
"telnet/udp" -> "telnet 23/udp"[[BR]]
Right now, the assumption is made that we're mapping N keys to at most one value. My current thinking is that the map code can be extended from taking a set of keys and one value to taking a set of keys and a matching set of values (or some set of values that we iterate over as we pass over keys, where the value chosen is the N % n_values one). The formatting code might even already do the right thing here.