Clean up the backups package.
Address review comments from axw.
Rename backup to backups.
Clean up DBConnInfo a bit.
Add a test for the files that will be backed up.
Move runCommand() to core utils.
Escalate log levels in backups and add more logged info.
Clarify the use of the path separator in backups.
Stop using named return arguments in backup's prepareTemp.
Use NewHashingWriter instead of NewSHA1Proxy.
Clarify what is going on when we build the backup tarball.
Fix order of operations in backups test setup.
Fix formatting in backups tests.
Clean up getFilesToBackup and pull out hard-coded paths.
Use the SameContents checker in backups tests.
Merge pull request #462 from ericsnowcurrently/backups-cleanup

Clean up the backups package.

This is intended as an idempotent change in preparation for further patches.