Add build option for using Visual Leak Detector for debugging memory leaks. Initial report:

- IfcConvert (no arguments): 2 leaks (140 bytes) (from OCE)
- IfcConvert (acad2010_objects.ifc): 47 memory leaks (6,158 bytes)
- IfcGeomServer: 2 leaks (from OCE)
- IfcOpenHouse: 11,952 leaks (1,169,658 bytes)!
- IfcParseExamples (acad2010_objects.ifc): 40 memory leaks (4,564 bytes)

src/examples/IfcOpenHouse.cpp

@@ -41,6 +41,10 @@
 #include "../ifcparse/IfcHierarchyHelper.h"
 #include "../ifcgeom/IfcGeom.h"
 
+#if USE_VLC
+#include <vld.h>
+#endif
+
 // Some convenience typedefs and definitions. 
 typedef std::string S;
 typedef IfcParse::IfcGlobalId guid;
@@ -531,6 +535,8 @@ void createGroundShape(TopoDS_Shape& shape) {
 	TColStd_Array1OfInteger mult(0, 1);
 	mult(0) = 5;
 	mult(1) = 5;	
+#undef new
+
 	Handle(Geom_BSplineSurface) surf = new Geom_BSplineSurface(cv, knots, knots, mult, mult, 4, 4);
 #if OCC_VERSION_HEX < 0x60502
 	shape = BRepBuilderAPI_MakeFace(surf);