Added msleep() on reload to allow new processes to start.

This is expected to ensure smoother operation on reload (and with less
chance of listen queue overflows).

Prodded by Igor Sysoev.

src/os/unix/ngx_process_cycle.c

@@ -250,6 +250,10 @@ ngx_master_process_cycle(ngx_cycle_t *cycle)
             ngx_start_worker_processes(cycle, ccf->worker_processes,
                                        NGX_PROCESS_JUST_RESPAWN);
             ngx_start_cache_manager_processes(cycle, 1);
+
+            /* allow new processes to start */
+            ngx_msleep(100);
+
             live = 1;
             ngx_signal_worker_processes(cycle,
                                         ngx_signal_value(NGX_SHUTDOWN_SIGNAL));