Mesh addition, removal and addition with the same name shows the first mesh

**Original report ([archived issue](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-rendering/issues/27)) by Agustin Alba Chicar (Bitbucket: [eku-agalbachicar](https://bitbucket.org/%7Bf3bbaa08-99e1-49b3-8f98-5b977c6eba97%7D/)).**

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After loading a `Mesh` into a `Scene`, it may be needed to remove it and then add a new `Mesh` with the same name but a different _shape_. If this is the case, the second time the mesh is loaded into the `Scene` the output shows the first one (i.e. first I add a cube called "mesh", then I remove the cube, then I add a cone whose name is "mesh" too, finally it shows cube instead of a cone).

In the meantime, I appended an increasing counter to the mesh names so they are unique and that made it work.

Note also that meshes are created at runtime but not loaded from a file.

I am working with Ogre, I couldn't test it in Optix.