* release the read lock earlier as it is not needed for chaincomputebasefee
* chain/messagepool/selection.go change to read lock in SelectMessages
* tighten up locks in chain/messagepool/repub.go and two questions on whether curTsLks are needed as comments
* include suggestion from @Jorropo to preallocate our msgs array so that we only need to make a single allocation
* mp.pending should not be accessed directly but through the getter
* from @arajasek: just check whether the sender is a robust address (anything except an ID address is robust) here, and return if so. That will:
be faster
reduce the size of this cache by half, because we can drop mp.keyCache.Add(ka, ka) on line 491.
* do not need curTslk and clean up code comments
Previously, we checked message gas/validity with the previous block's
height. This doesn't affect consensus, but will help us avoid adding
messages to the message pool that shouldn't be there.
