version 4/080915 by Mikael Segercrantz
Section 2a16 - Before going port (for use with Shipboard Directions by Mikael Segercrantz)
Before going port:
let table-of-exits be exits port of the location;
if the number of filled rows in table-of-exits is 0, continue the action;
modify the port exit of the location according to table-of-exits.