Merge branch 'ENG-5712' into ENG-5799
ENG-5799 clean up volt compiler error messages.
ENG-5799 Got rid of a pointless error message.
ENG-5967: Log when snapshot streamMore() returns an error.

Print out the type of the error as well as the table name.
Retry helper should take max attempts into account. Throw a RuntimeException if
the max attempt has been reached.
Reset row position after unioning the tables in the helper class.
ENG-5843: Moving pre-snapshot scan to a dedicated IO agent.

The SnapshotDaemon will dispatch a scan work to the snapshot IO agent on each
node before initiating a snapshot. If the check fails, the snapshot will not be
initiated.
ENG-5715: Clean up:
Remove dead code.
Delete RoadBlocks from RPQ
Delete unused method for DR
Delete unused field
Remove unused isHeartbeat argument
ENG-5715: Use the globally safe TXN ID to release transactions from
the AgreementSite's RestrictedPriorityQueue.  Ensures that synchronous
ZK writes only return when they've been witnessed by all nodes.
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-5799
Merge pull request #1177 from VoltDB/eng5715

Eng5715
Merge pull request #1178 from VoltDB/ENG-5799

ENG-5799 Improve compilation messages.
Merge pull request #1171 from VoltDB/ENG-5967

ENG-5967: Log when snapshot streamMore() returns an error.
ENG-5843: Don't spin the SnapshotDaemon thread when waiting for scan results.
ENG-5843: Timeout waiting for scan results in SnapshotDaemon.
Merge pull request #1173 from VoltDB/ENG-5843

ENG-5843: Move snapshot scan out of SnapshotSave