Session handlers should probably be plugable.
Refs #1565: define a pluggable session storage interface.
Refs #1565: dbs don't automatically handle sessions
Refs #1565: these classes implement the appropriate interface
Closes #1565: making session storage plugable, with file fallback.
We don't want to save session handler stuff in config
Make handleSession() a little bit more useful. Should return true if …
…the session was handled.
This allows sessions which require certain preconditions to fail gracefully back to files.