Fix ignored headers handling in fastcgi/scgi/uwsgi.

The bug had appeared in r3561 (fastcgi), r3638 (scgi), r3567 (uwsgi).

Fix buffer overrun under Windows.

Proxy related fixes:

*) finalizing with rc == 0 in unbuffered proxy mode caused nginx to wait
   for another send_timeout before actually closing client's connection
   if client timed out while still talking to upstream server
*) update r3945 with more descriptive error message
*) test length of proxy_pass with variables;
   patch by Lanshun Zhou

Lingering closing related fixes:

*) lingering_close "off|on|always"
*) enable lingering close for pipelined requests
*) do not send RST on normal lingering close read timeout,
   if reset_timedout_connection is on

SSL related fixes:

*) MSIE export versions are rare now, so RSA 512 key is generated on demand
   and is shared among all hosts instead of pregenerating for every HTTPS host
   on configuraiton phase. This decreases start time for configuration with
   large number of HTTPS hosts.
*) ECDHE support; patch by Adrian Kotelba
*) fix build by gcc46 with -Wunused-value option
*) fix SSL connection issues on platforms with 32-bit off_t
*) do not try to reuse and save a SSL session for a peer created on the fly
   by ngx_http_upstream_create_round_robin_peer(), since the peer lives
   only during request so the saved SSL session will never be used again
   and just causes memory leak

Accept-Encoding refactoring:
*) "gzip; q=0" support
*) and removal of ancient MSIE 4.x test for gzip

Cache fixes:

*) do not close connection if cache file is too small: replace it with
   valid one
*) rename ngx_http_file_cache_manager_sleep() to
   ngx_http_file_cache_loader_sleep() and do not use it all in cache manager:
   this is a vestige of the times when cache manager loaded cache
*) set correct configuration file values while adding path

Cache loader improvements:

The cache loader performs two tasks: inserting cache objects in inactivity
list and evaluating total cache size. Reading just directory is enough for
this purpose. Elimination of reading cache files saves at least one disk I/O
operation per file.

Cache size accounting fix: actual cache size on disk was less than
needed by sum of sizes of files loaded by worker processes themselves
while cache loader was running.

The bug has been introduced in r3900.