Previously, the default pool alignment used sizeof(unsigned long), with
the expectation that this would match to a platform word size.  Certain
64-bit platforms prove this assumption wrong by keeping the 32-bit long
type, which is fully compliant with the C standard.

This introduces a possibility of suboptimal misaligned access to the
data allocated with ngx_palloc() on the affected platforms, which is
addressed here by changing the default NGX_ALIGNMENT to a pointer size.

As we override the detection in auto/os/conf for all the machine types
except x86, and Unix-like 64-bit systems prefer the 64-bit long, the
impact of the change should be limited to Win64 x64.

When enabled, some structures are padded to be size compatible
with their NGINX Plus versions.

It was broken since introduction (__GNU__ instead of __GNUC__) and did
nothing.  Moreover, GCC 2.7 is happy with the normal version of the code.

Reported by Joel Cunningham,
http://mailman.nginx.org/pipermail/nginx-devel/2016-March/007964.html.

These are needed to detect overflows.

patch by Maxim Dounin

*) use ngx_snprintf() in ngx_inet_ntop() and ngx_sock_ntop()
   as they are called just once per connection
*) NGX_INET_ADDRSTRLEN

*) Darwin sendfile() support