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.
We do, but the log line points to code in process.cc which makes the statements very uninteresting. This macro puts the correct file name and line numbers next to the commands, and since so much of this ends up being just shell code its easier to trace.