* Verify accepted ledger becomes validated, and retry
   with a new consensus transaction set if not.
 * Always store proposals.
 * Track proposals by ledger sequence. This helps slow peers catch
   up with the rest of the network.
 * Acquire transaction sets for proposals with future ledger sequences.
   This also helps slow peers catch up.
 * Optimize timer delay for establish phase to wait based on how
   long validators have been sending proposals. This also helps slow
   peers to catch up.
 * Fix impasse achieving close time consensus.
 * Don't wait between open and establish phases.

…nsus

* upstream/develop:
  feat: support Concise Transaction Identifier (CTID) (XLS-37) (4418)