Rewrite: removed r->err_status special handling (ticket #1634).

Trying to look into r->err_status in the "return" directive
makes it behave differently than real errors generated in other
parts of the code, and is an endless source of various problems.
This behaviour was introduced in 726:7b71936d5299 (0.4.4) with
the comment "fix: "return" always overrode "error_page" response code".
It is not clear if there were any real cases this was expected to fix,
but there are several cases which are broken due to this change, some
previously fixed (4147:7f64de1cc2c0).

In ticket #1634, the problem is that when r->err_status is set to
a non-special status code, it is not possible to return a response
by simply returning r->err_status.  If this is the case, the only
option is to return script's e->status instead.  An example
configuration:

    location / {
        error_page 404 =200 /err502;
        return 404;
    }

    location = /err502 {
        return 502;
    }

After the change, such a configuration will properly return
standard 502 error, much like it happens when a 502 error is
generated by proxy_pass.

This also fixes the following configuration to properly close
connection as clearly requested by "return 444":

    location / {
        error_page 404 /close;
        return 404;
    }

    location = /close {
        return 444;
    }

Previously, this required "error_page 404 = /close;" to work
as intended.

src/http/modules/ngx_http_rewrite_module.c

@@ -180,15 +180,7 @@ ngx_http_rewrite_handler(ngx_http_request_t *r)
         code(e);
     }
 
-    if (e->status < NGX_HTTP_BAD_REQUEST) {
-        return e->status;
-    }
-
-    if (r->err_status == 0) {
-        return e->status;
-    }
-
-    return r->err_status;
+    return e->status;
 }