Merge of r3960, r3961, r3962, r3963, r3965:

Merge of r3960, r3961, r3962, r3963, r3965:

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