Blender Git Loki

Add argument to DM_to_mesh() function to take ownership over the DM

The idea is pretty simple: instead of making temporary copy of all the
related custom data layers just pass the ownership from the DM to the
mesh.

This is really handy in cases when you've got DM which you need to
convert to Mesh datablock and wouldn't need that DM after conversion
anyway.

Foe example, render database conversion, exporters and even Modifier
Apply will benefit from this option.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D1127