Try and get NxN to work again.

- Moved NxN search to be done on the same level as other searches, as it's
  really not any different from 2Nx2N.
- Produces working bitstream but reconstruction is different.
Set correct max depth for search work-tree copying.

The copy up and down functions had wrong max depth so they didn't work with
4x4 blocks.
Fix bug with selecting wrong coeff scan mode for 4x4 blocks.
Merge branch 'intra-NxN'

Conflicts:
	src/search.c