Sketcher needs collision tests.

[kayabaNerve]

If Meros has a collision internally, it should generate a new salt for the template. If Meros has a collision internally, yet is syncing, it should fail to handle the sketch yet still successfully sync the Block, as long as it doesn't have a collision.

Meros should also be to handle being sent Blocks with a collision. Due to the set theory used for sketches, it's impossible to include a sketch with the same item twice. That said, it is still possible to create a sketchCheck merkle with the same values twice, and therefore a Block Header.