Applying proposer boost to ancestors

[realbigsean]

It looks like the proposer score boost is not applied to ancestors of the boosted block, even during the boosted block's slot. Is this the correct behavior?

This is highlighted by the test scenario: shorter_chain_but_heavier_weight

In that scenario, during slot 3, there is a proposer-boosted block from slot three, as well as a late-arriving block from slot 1. The test expects the block from slot 1 to be set as head, even when they are tied in attestation weight (at zero). I'd expect the get_head method to incorporate the proposer boost and set block 3 as head.