Construct orco UV layer for curve when applying constructive modifier
Also construct orco uv layer when converting curve to a mesh.

This makes it possible to preserve automatically generated coordinates
("use uv for mapping" option) when using constructive modifiers or
converting curve to the mesh.

With cycles nothing special is needed to preserve texture mapping
after such operations, in blender internal you'll need to change
texture mapping from Generated to UV.

This feature is useful on it's own and also would help in potential
switch 3d viewport to always use DM to draw objects, which would
help making drawing more thread-safe.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57609 954f8c5b-7b00-dc11-b283-0030488c597c