Use fast COPY ... FROM STDIN for writing log tables.

Also implement a couple of other compression methods (no compression and
deflate (at BEST_SPEED)).  We've been seeing segfaults in the data
coordinator during big uploads, and since Snappy's the only native code
on that codepath, I'm trying swapping it out for other things.
Update snappy
Reduce log-writing target time to 1 second
Only update lastBatchSize if it's been changed

An attempt to minimize in-fighting between simultaneous log-writers
Use protobufs instead of a custom format for the log's "aux" field
Close the PostgresUniverse, not just the connection

This is important now that Loggers hold a temp file
DRY the two SQL-based loggers
Add (and use) pure Java snappy