Operational mode (op_mode in the database) affects the state diagram
and timeouts for a node. Modes planned so far are:
NORMAL    - Normal operation
DELAYING  - Acting as a delay node
UNKNOWNOS - Running an OS that does not report its state (OSKit kernels, etc.)
RELOADING - Disk reloading

stated now responds to to TBNODEOPMODE events, and sets database state
accordingly. The set of state timeouts and valid state transitions are
affected by a node's operational mode.

The nodes table now stores information about operational modes, and
the state_transitions and state_timeouts tables include the operational
mode in addition to states.

Next step will be to get the appropriate programs to send TBNODEOPMODE
events.