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().