mail related fixes:

*) delete surplus code
*) Zimbra IMAP server may return only 4 bytes: "+ \r\n"

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

resolver fixes:

*) fix memory leak in resolver
*) fix resolver cache rbtree comparison
*) fix segfault in resolver:
   ngx_resolve_name_done() and ngx_resolve_addr_done() did not delete
   contexts from a resolver node waiting list.
*) fix "PTR ." case in address resolver
*) add quotes in an error message,
*) fix resolving an empty name (".")
*) use ngx_resolver_alloc() instead of ngx_resolver_calloc()
   since all fields are filled

various SSL fixes and features:

*) $ssl_client_verify
*) "ssl_verify_client ask" was changed to "ssl_verify_client optional"
*) ssl_crl
*) delete OpenSSL pre-0.9.7 compatibility: the sources were not actually
   compatible with OpenSSL 0.9.6 since ssl_session_cache introduction
*) fix memory corruption in $ssl_client_cert
*) issue SNI warning instead of failure: this is too common case
*) use ngx_log_error(), since OpenSSL does not set an error on the failure
*) add SNI support in -V output

fix various failures handling

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