allow to "set" $http_, $sent_http_, and $upstream_http_ variables

src/http/modules/ngx_http_rewrite_module.c

diff --git a/src/http/modules/ngx_http_rewrite_module.c b/src/http/modules/ngx_http_rewrite_module.c
index 274991e..1b660c3 100644
--- a/src/http/modules/ngx_http_rewrite_module.c
+++ b/src/http/modules/ngx_http_rewrite_module.c
@@ -935,7 +935,11 @@
         return NGX_CONF_ERROR;
     }
 
-    if (v->get_handler == NULL) {
+    if (v->get_handler == NULL
+        && ngx_strncasecmp(value[1].data, "http_", 5) != 0
+        && ngx_strncasecmp(value[1].data, "sent_http_", 10) != 0
+        && ngx_strncasecmp(value[1].data, "upstream_http_", 14) != 0)
+    {
         v->get_handler = ngx_http_rewrite_var;
         v->data = index;
     }