Win32: disabled MSVC warning about '\0' not fitting into array.

We believe that this warning produces more inconvience than real benefit.
Here is an example to trigger:

  u_char a[4] = "test";


git-svn-id: svn://svn.nginx.org/nginx/trunk@5121 73f98a42-aea0-e011-b76d-00259023448c