Improved exception text for undefined macro in scatterfile.

Author: cw2

Framework/Tools/BuildTasks/ScatterFile.cs

@@ -501,8 +501,14 @@ string Resolve( Hashtable seen, string val )
 
                     seen[var] = true;
 
+                    var varName = var;
                     var = Resolve( seen, GetVariable( var ) );
 
+                    if(var == null)
+                    {
+                        throw Document.ParseException( "'{0}' is not defined", varName );
+                    }
+
                     seen.Remove( var );
                 }