After the upgrade, we're allowed to use randomness up to the challenge epoch.
This safe-guards us against very large reorgs where a miner computes a PoSt very
quickly.
Method numbers never change anyways. At worst, we'll deprecate old methods and
have to explicitly import them from the correct actors version to use them.
* We may have multiple sectors with the same size and different proof types, but all these management functions stay the same.
* This simplifies PoSt logic.
Motivation:
* Run lotus with the race detector enabled (primary motivation).
* Allow multiple lotus nodes in a process (not a high priority).
Previously, the journal was shared between all lotus instances, but it was
initialized for every new node. This caused safety problems in tests (at a
minimum).
This patch explicitly passes the journal to all services that need it.
