[PATCH 2 of 5] Fix error_page status code change in redirect

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1288669812 -10800
# Node ID 49670f58d178cbef2108a76676b8d79cf2cb648b
# Parent  1e3045c3de6be5718359f4e0e3af9007f3da50aa
Fix error_page status code change in redirect.

Using codes other than 301, 302 and 303 resulted in unexpected behaviour.  E.g.
something like

    error_page 404 =200 http://localhost/;

resulted in "[alert] ... writev() failed (14: Bad address)" messages and no
reply returned.  See here for initial report:

http://nginx.org/pipermail/nginx-ru/2010-October/037506.html

The same problem appears when redirecting special error codes which has
implict code changes, e.g. 497.  See here for report:

http://nginx.org/pipermail/nginx/2010-November/023402.html

diff --git a/src/http/ngx_http_special_response.c b/src/http/ngx_http_special_response.c
--- a/src/http/ngx_http_special_response.c
+++ b/src/http/ngx_http_special_response.c
@@ -557,7 +557,14 @@ ngx_http_send_error_page(ngx_http_reques
         return NGX_ERROR;
     }
 
-    r->err_status = overwrite > 0 ? overwrite : NGX_HTTP_MOVED_TEMPORARILY;
+    if (overwrite >= NGX_HTTP_MOVED_PERMANENTLY
+        && overwrite < NGX_HTTP_LAST_LEVEL_300)
+    {
+        r->err_status = overwrite;
+
+    } else {
+        r->err_status = NGX_HTTP_MOVED_TEMPORARILY;
+    }
 
     location->hash = 1;
     ngx_str_set(&location->key, "Location");