Convert back temporary mesh created with to_mesh() to normal mesh

Hello guys,

@ideasman42 I was wandering if temporary mesh created with to_mesh() API can be converted back to a “normal” mesh which can be added then to the main database. I know aboud `new_from_object(), but this one works at object level and you can’t specify temporary mesh as alternative to the default mesh

It would be nice to have a mesh.extend(another_mesh) API at python level. That would fix this problem and also add the possibility to merge meshes at mesh level. Another important feature missing from the current python API…