Use absolute path names only for directories containing slowly-changing
library modules.
+A path is considered ``absolute'' if it starts with ``@/@'', or
+``@A:/@'', or ``@A:\@'' (or ``@B:/@'', ``@B:\@'' etc).
+
Patrick Sansom had a workshop paper about how all this is done (though
the details have changed quite a bit). Ask
him (email: <htmlurl name="sansom@@dcs.gla.ac.uk"