Mantis#1931. Thank you kindly, Kinoc for a patch that:

* Yield Prolog 1.0.1 Released : it passes all but 9 of the 
421 tests in the ISO Prolog test suite (97.8%) .
* support dynamic predicates and rules.
* support 'import' to use external static functions 
improves connection to C# functions
* Matches Yield Prolog r831

OpenSim/Region/ScriptEngine/DotNetEngine/Compiler/YieldProlog/Functor.cs

@@ -98,6 +98,14 @@ namespace OpenSim.Region.ScriptEngine.DotNetEngine.Compiler.YieldProlog
             return make(Atom.a(name), args);
         }
 
+        /// <summary>
+        /// If arg is another Functor, then succeed (yield once) if this and arg have the
+        /// same name and all functor args unify, otherwise fail (don't yield).
+        /// If arg is a Variable, then call its unify to unify with this.
+        /// Otherwise fail (don't yield).
+        /// </summary>
+        /// <param name="arg"></param>
+        /// <returns></returns>
         public IEnumerable<bool> unify(object arg)
         {
             arg = YP.getValue(arg);