toplev: read from /dev/urandom only when needed

toplev: read from /dev/urandom only when needed

	* toplev.h (set_random_seed): Adjust return type.
	* toplev.c (init_local_tick): Move eager initialization of random_seed
	to get_random_seed.  Adjust comment.
	(init_random_seed): Inline to get_random_seed, delete.
	(get_random_seed): Initialize random_seed lazily.
	(set_random_seed): Do not return previous value.
	(print_switch_value): Do not call get_random_seed.

From-SVN: r253069