fix segfault if there is error_page 401, proxy_intercept_errors is on
and backend does not return "WWW-Authenticate" header

ignore ngx_atomic_fetch_add() result
this fixes building at least by gcc 4.2.1 on Mac OS X 10.6

cache related fixes:

*) fix building --without-http-cache, broken in r2945
*) fix ./configure error message

r2909, r2910, r2922, r2923, r2924, r2925, r2929:

various win32 fixes:

*) use no-threads for Unix builds only
*) Win32 returns ERROR_PATH_NOT_FOUND instead of ERROR_FILE_NOT_FOUND
*) add trailing zero to a file name in ngx_win32_rename_file()
*) fix logging in ngx_win32_rename_file()
*) allow shared memory segments more than 4G
*) fix memory leak in successful case
*) log shared memory name in failure case
*) test that zone has the same addresses in different processes
*) add drive letter for Win32 root path
*) log GetExitCodeProcess()'s errno
*) test premature process termination
*) fix debug logging
*) exit if no workers could not be started
*) do not quit old workers if no new workers could not be started
*) a signaller process should stop configuration processing just after
   it is able to get pid file, this allows to not open log files, etc.
*) win32 master process had aready closed listening sockets

various proxy/fastcgi cache features and fixes:

*) report about proxy/fastcgi_store and proxy/fastcgi_cache incompatibility
*) delete useless r->cache->uses
*) proxy_cache_use_stale/fastcgi_cache_use_stale  updating
*) inherit proxy_set_header, proxy_hide_header, and fastcgi_hide_header
   only if cache settings are similar
*) add response file uniq while loading cold cache on demand

test GIF87a