diff -r 3b71e57fd22b -r a749c78812a7 src/cargotype.cpp
--- a/src/cargotype.cpp	Fri Feb 23 08:37:33 2007 +0000
+++ b/src/cargotype.cpp	Fri Feb 23 09:56:20 2007 +0000
@@ -67,3 +67,9 @@
 	assert(_cargo_bitnum_map[bitnum] != CT_INVALID);
 	return _cargo_bitnum_map[bitnum];
 }
+
+
+bool CargoSpec::IsValid() const
+{
+	return bitnum != INVALID_CARGO;
+}