Resolved warnings about declarations that hide previous local declarations.
Warnings about WSASocketA() being deprecated resolved by explicit use of
WSASocketW() instead of WSASocket().  When compiling without IPv6 support,
WinSock deprecated warnings are disabled to allow use of gethostbyname().

Iterating through all connections takes a lot of CPU time, especially
with large number of worker connections configured.  As a result
nginx processes used to consume CPU time during graceful shutdown.
To mitigate this we now only do a full scan for idle connections when
shutdown signal is received.

Transitions of connections to idle ones are now expected to be
avoided if the ngx_exiting flag is set.  The upstream keepalive module
was modified to follow this.

Two mechanisms are implemented to make it possible to store pointers
in shared memory on Windows, in particular on Windows Vista and later
versions with ASLR:

- The ngx_shm_remap() function added to allow remapping of a shared memory
  zone to the address originally used for it in the master process.  While
  important, it doesn't solve the problem by itself as in many cases it's
  not possible to use the address because of conflicts with other
  allocations.

- We now create mappings at the same address in all processes by starting
  mappings at predefined addresses normally unused by newborn processes.

These two mechanisms combined allow to use shared memory on Windows
almost without problems, including reloads.

Based on the patch by Sergey Brester:
http://mailman.nginx.org/pipermail/nginx-devel/2015-April/006836.html