NV18: Implement state checks for new actors

[arajasek]

These are currently unimplemented for the 4 new actors: https://github.com/filecoin-project/builtin-actors/blob/next/state/src/check.rs#L223-L226. For actors where no state check is possible, explicitly say so in a comment.

Also examine the init actor's state check for any necessary updates.

[arajasek]

Note that Lotus has already implemented some of these in Go in order to sanity check the nv18 changes: https://github.com/filecoin-project/go-state-types/tree/master/builtin/v10.

[jennijuju]

is this still needded?

[anorth]

is this still needded?

If they're not done yet, yes.