FIP 41 - Forward Compatibility for PreCommit and ReplicaUpdate

[lemmih]

Issue summary

• [x] Are there any changes to the actor data structures that we need to be aware of?
• [x] Are there any changes to the network protocol?
• [x] Are there any changes to node behavior (eg. changes in block validation criteria, random number generation, etc)?
• [x] Are there any new magic numbers?

Other information and links

https://github.com/filecoin-project/FIPs/blob/master/FIPS/fip-0041.md

[LesnyRumcajs]

The only data structure change we need to implement is SectorPreCommitInfo which would be already covered by FIP0034. So all in all, FIP0041 is a subset of FIP0034 - implementing FIP0034 will complete this one.