Perl: fixed delaying subrequests.

Much like in limit_req, use the wev->delayed flag to ensure proper handling
and interoperability with limit_rate.

src/http/modules/perl/nginx.xs

diff --git a/src/http/modules/perl/nginx.xs b/src/http/modules/perl/nginx.xs
index 6716620..cca64da 100644
--- a/src/http/modules/perl/nginx.xs
+++ b/src/http/modules/perl/nginx.xs
@@ -1001,6 +1001,7 @@
 
     ctx->next = SvRV(ST(2));
 
+    r->connection->write->delayed = 1;
     ngx_add_timer(r->connection->write, sleep);
 
     r->write_event_handler = ngx_http_perl_sleep_handler;

src/http/modules/perl/ngx_http_perl_module.c

diff --git a/src/http/modules/perl/ngx_http_perl_module.c b/src/http/modules/perl/ngx_http_perl_module.c
index 2796319..79ded0f 100644
--- a/src/http/modules/perl/ngx_http_perl_module.c
+++ b/src/http/modules/perl/ngx_http_perl_module.c
@@ -278,15 +278,19 @@
 
     wev = r->connection->write;
 
-    if (wev->timedout) {
-        wev->timedout = 0;
-        ngx_http_perl_handle_request(r);
+    if (wev->delayed && !wev->timedout) {
+
+        if (ngx_handle_write_event(wev, 0) != NGX_OK) {
+            ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
+        }
+
         return;
     }
 
-    if (ngx_handle_write_event(wev, 0) != NGX_OK) {
-        ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
-    }
+    wev->delayed = 0;
+    wev->timedout = 0;
+
+    ngx_http_perl_handle_request(r);
 }