export geom.Mat4 copy constructor

modules/geom/pymod/export_mat4.cc

@@ -114,6 +114,7 @@ void export_Mat4()
     .def(init<Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real,Real>())
     .def(init<const Mat2&>())
     .def(init<const Mat3&>())
+    .def(init<const Mat4&>())
     .def(self += self)
     .def(self -= self)
     .def(self + self)