switch to using isc_loopmgr_pause() instead of task exclusive

change functions using isc_taskmgr_beginexclusive() to use
isc_loopmgr_pause() instead.

also, removed an unnecessary use of exclusive mode in
named_server_tcptimeouts().

most functions that were implemented as task events because they needed
to be running in a task to use exclusive mode have now been changed
into loop callbacks instead. (the exception is catz, which is being
changed in a separate commit because it's a particularly complex change.)

lib/isc/loop.c

@@ -597,3 +597,10 @@ isc_loopmgr_nonblocking(isc_loopmgr_t *loopmgr) {
 	isc_signal_start(loopmgr->sigint);
 	isc_signal_start(loopmgr->sigterm);
 }
+
+isc_loopmgr_t *
+isc_loop_getloopmgr(isc_loop_t *loop) {
+	REQUIRE(VALID_LOOP(loop));
+
+	return (loop->loopmgr);
+}