open_file_cache related fixes:

*) Bugfix: open_file_cache lost is_directio flag.

On file retest open_file_cache lost is_directio if file wasn't changed.
This caused unaligned operations under Linux to fail with EINVAL.
It wasn't noticeable with AIO though, as errors wasn't properly logged.

*) Bugfix: open_file_cache did not update file info on retest.

If file inode was not changed, cached file information was not updated
on retest.  As a result stale information might be cached forever if file
attributes was changed and/or file was extended.

A new fix for the case when ssl_session_cache defined, but ssl is not
enabled in any server. The previous r1033 does not help when unused zone
becomes used after reconfiguration, so it is backed out.

The initial thought was to make SSL modules independed from SSL implementation
and to keep OpenSSL code dependance as much as in separate files.

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

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.