Implement "quick" shutdown (similiar in behavior to shutdown

Implement "quick" shutdown (similiar in behavior to shutdown
prior to connection management changes).  No "normal" (wait
for pending operations to complete) shutdown mode (yet).
Changes:
 Add connections_destroy() implementation to connections.c.
 Move connections_init() call to slap_daemon().
 Add connections_destroy() call to slap_daemon().
 Add connections_shutdown() implementation to connections.c.
	calls connection_closing()/connection_close() for each
	"in use" connection.
 Add connections_shutdown() call to slap_daemon_task().