Update comment in lwan_thread_shutdown()

epoll_wait() will always timeout every second if there are items
in a respective thread's death queue. Previously it would wait until
lwan->config->keep_alive_timeout seconds, but this changed ages
ago.
Pass base 0 to strtol() in parse_long()

The correct base should be guessed from the contents when base 0
is passed to strtol(), so yanking the base detection code is safe
(except for binary base, which is kind of useless anyway, given
hexadecimal values are allowed).