Fixing proxy_set_body and proxy_pass_request_body with SSL.

Flush flag wasn't set in constructed buffer and this prevented any data
from being actually sent to upstream due to SSL buffering.  Make sure
we always set flush in the last buffer we are going to sent.

See here for report:
http://nginx.org/pipermail/nginx-ru/2011-June/041552.html

src/http/modules/ngx_http_proxy_module.c

@@ -1132,12 +1132,11 @@ ngx_http_proxy_create_request(ngx_http_request_t *r)
             body = body->next;
         }
 
-        b->flush = 1;
-
     } else {
         u->request_bufs = cl;
     }
 
+    b->flush = 1;
     cl->next = NULL;
 
     return NGX_OK;