Prevent release build on Visual Studio 12 from throwing compiler error C2504.

Thanks to Kristoffer Josefsson for the patch.

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@255 66977474-1d4b-4f09-8fe9-267525286df2

src/OpenVolumeMesh/Core/PropertyDefines.hh

@@ -49,6 +49,7 @@
 
 #include "BaseProperty.hh"
 #include "PropertyHandles.hh"
+#include "PropertyPtr.hh"
 
 namespace OpenVolumeMesh {