Blender Git Loki

Subdiv: CCG, store edge adjacency information

This information is stored for each non-loose edge.

For each of such edge we store:

- List of CCG faces it is adjacent to.

This way we can easily check whether it is adjacent to
any face which is tagged for update or so.

- List of boundary elements from adjacent grids.

This allows to traverse along the edge and average all
adjacent grids.