Drinker sessions: fix bad merge.

Closes #262.
stats: Generate missing records when needed.
Update kb_regen_sessions.
stats: Quiet logs.
plugin: Log and suppress errors during plugin event dispatch.
backup: Initial work-in-progress.
backup: Initial support for 'restore'.

Still needed:
 - Postgres truncate/reset support.
 - Unittests.
backup: Clean up logs.
backup: Print full file path when available.
backup: Add backup_format; add unittest.
backup: test generated backup equality.