Added Redis backup and restore capabilities

Currently limited to rdb and doesn't muck with config files.
Refactored large portions of MySQL backup code to share whatever
the two datastores had in common.
Finished Redis backup code

* Changed the log to show what thread did what, as it was driving
  me crazy.
* Added a flag to allow a master to do a backup. Otherwise the
  integration tests won't work. :-p
* Had to add a lot of logic to ensure Redis had finished writing to
  the directory after a successful bgsave.
Merge pull request #95 from TimSimpsonR/redis-backups-2

Added Redis backup and restore capabilities