fix negative time in "Cache-Control" if "expires modified" sets time in the past

perl exit fixes:

*) use global perl variable in perl_destruct()/perl_free()
   for non-mulitiplicity perl
*) add comment from r2716 commit message

gzip headers related fixes:

*) remove "Content-Encoding: gzip" in 304 response
   sent by ngx_http_gzip_static_module
*) refactor gzip_vary handling
*) test r->header_only last, since it's not actually
   frequent here: 304 and HEAD responses are not set it before the filter

cache related fixes:

*) do not pass buf with empty cached response,
   this fixes "zero size buf in output" alert
*) hide cacheable Set-Cookie and P3P FastCGI response headers
*) test comma separator in "Cache-Control"
*) a cache manager thread handle was overwritten by a cache loader thread
   handle, this caused an exit delay, the bug had been introduced in r3248
*) fix handling cached HTTP/0.9 response
*) log proxied HTTP/0.9 responses status as "009"
*) fix the "If-None-Match" header name
*) fix a cached zero-length body case

fix segfault if $limit_rate was logged
fix segfault in SSL if limit_rate is used

      r3202, r3203, r3383, r3388, r3417, r3418:

Win32 (mostly) and some Unix file related fixes:

*) preserve errno while ngx_free()
*) win32 ngx_file_info() utf8 support
*) delete Win95 code
*) log file name for read/write errors
*) test incomplete WriteFile()
*) handle short pwrite() to log an error cause: ENOSPC, EDQUOT, or EFBIG
*) uniform ngx_directio_on/off() interface with other file functions
*) do not create Win32 drive letter in ngx_create_full_path()
*) ignore EACCES errors for top level directories in ngx_create_full_path()
*) fix Win32 error messages when an temporary file replaces an existent file:
   *) do not rename an already renamed file
   *) now ngx_win32_rename_file() returns error code
   *) do not log failure inside ngx_win32_rename_file()
*) fix Win32 error message when an temporary file replaces an existent file:
   return at once if ngx_win32_rename_file() was not failed
   and do not try to delete already the renamed temporary file
*) skip URI trailing spaces under Win32
*) disable Win32 short file names

ngx_http_parse_time() fixes:

*) use ngx_uint_t instead of int,
   strange to say this reduce function size by 16 bytes
*) ngx_http_parse_time() should support full 32-bit time

ngx_http_autoindex_module fixes:

*) reset cached dirent.d_type after stat()
   this fixes slash after link to a directory in ngx_http_autoindex_module;
*) use cached dirent.d_type as hint on all systems

   the issues has been introduced in r2235

*) fix ngx_utf8_cpystrn(): it did not fully copy utf-8 string

*) fix discarding body
*) prevent handling discarded body as a pipelined request

SSL fixes:

*) $ssl_session_id
*) allow "make clean" for OpenSSL, the bug was introduced in r2874
*) disable SSLv2 and use only strong ciphers by default
*) decrease SSL handshake error level to info