don't require log-mode to auto-respawn

don't require log-mode to auto-respawn

Don't require log-mode (and more importantly, subclasses thereof) to respawn.
If a buffer name is provided during initialization, respawning will be on;
otherwise, it will be off. Now e.g. console mode can use log-mode without
requiring a buffer name, or incurring potentially weird auto-respawn behavior.