Configure: help updated to list upstream keepalive and least_conn.

Patch by Joshua Zhu.

auto/options

diff --git a/auto/options b/auto/options
index 191d6c8..a75bead 100644
--- a/auto/options
+++ b/auto/options
@@ -388,6 +388,10 @@
   --without-http_browser_module      disable ngx_http_browser_module
   --without-http_upstream_ip_hash_module
                                      disable ngx_http_upstream_ip_hash_module
+  --without-http_upstream_least_conn_module
+                                     disable ngx_http_upstream_least_conn_module
+  --without-http_upstream_keepalive_module
+                                     disable ngx_http_upstream_keepalive_module
 
   --with-http_perl_module            enable ngx_http_perl_module
   --with-perl_modules_path=PATH      set Perl modules path