python: expose buffer objects owned by gl.Mesh.

Makes testing much easier.

src/python/magnum/gl.cpp

@@ -24,6 +24,7 @@
 */
 
 #include <pybind11/pybind11.h>
+#include <pybind11/stl.h> /* for Mesh.buffers */
 #include <Corrade/Containers/ArrayView.h>
 #include <Corrade/Utility/FormatStl.h>
 #include <Magnum/GL/AbstractShaderProgram.h>
@@ -247,7 +248,8 @@ void gl(py::module& m) {
             self.draw(shader);
         }, "Draw the mesh")
         /** @todo more */
-        ;
+
+        .def_readonly("buffers", &PyMesh::buffers, "Buffer objects referenced by the mesh");
 
     /* Renderer */
     {

src/python/magnum/test/test_gl_gl.py

@@ -96,6 +96,8 @@ class Mesh(GLTestCase):
         # Adding a buffer to the mesh should increase its ref count
         mesh = gl.Mesh()
         mesh.add_vertex_buffer(buffer, 0, 8, gl.Attribute(gl.Attribute.Kind.GENERIC, 2, gl.Attribute.Components.TWO, gl.Attribute.DataType.FLOAT))
+        self.assertEqual(len(mesh.buffers), 1)
+        self.assertIs(mesh.buffers[0], buffer)
         self.assertEqual(sys.getrefcount(buffer), buffer_refcount + 1)
 
         # Deleting the mesh should decrease it again