On Windows, a worker process does not call ngx_slab_init() from
ngx_init_zone_pool(), so ngx_slab_max_size, ngx_slab_exact_size,
and ngx_slab_exact_shift were left uninitialized.

This also fixes potential undefined behaviour in the range and slice filter
modules, caused by local overflows of signed integers in expressions.

The error is fatal when configuring a new socket, so the ", ignored" part
is not appropriate and was removed.

When closing a socket with SO_REUSEPORT, Linux drops all connections waiting
in this socket's listen queue.  Previously, it was believed to only result
in connection resets when reconfiguring nginx to use smaller number of worker
processes.  It also results in connection resets during configuration
testing though.

Workaround is to avoid using SO_REUSEPORT when testing configuration.  It
should prevent listening sockets from being created if a conflicting socket
already exists, while still preserving detection of other possible errors.
It should also cover UDP sockets.

The only downside of this approach seems to be that a configuration testing
won't be able to properly report the case when nginx was compiled with
SO_REUSEPORT, but the kernel is not able to set it.  Such errors will be
reported on a real start instead.

It is safe because re-sending still works during graceful shutdown as
long as resolving takes place (and resolve tasks set their own timeouts
that are not cancelable).

Also, the new ctx->cancelable flag can be set to make resolve task's
timeout event cancelable.

No functional changes.