We don't have strong reason to inform about any errors
reported by close() call here, and there are no other things
to do with its return value.

Prodded by Coverity.

resolved address was used.  Now all addresses will be used.

This saves about 522K per connection.

if SSL buffer is not used.

In case of EMFILE/ENFILE returned from accept() we disable accept events,
and (in case of no accept mutex used) arm timer to re-enable them later.
With accept mutex we just drop it, and rely on normal accept mutex handling
to re-enable accept events once it's acquired again.

As we now handle errors in question, logging level was changed to "crit"
(instead of "alert" used for unknown errors).

Note: the code might call ngx_enable_accept_events() multiple times if
there are many listen sockets.  The ngx_enable_accept_events() function was
modified to check if connection is already active (via c->read->active) and
skip it then, thus making multiple calls safe.

Instead of checking if there is events{} section present in configuration
in init_module handler we now do the same in init_conf handler.  This
allows master process to detect incorrect configuration early and
reject it.