Events: added check for duplicate "events" directive.

src/event/ngx_event.c

diff --git a/src/event/ngx_event.c b/src/event/ngx_event.c
index 976bd64..cbae0ee 100644
--- a/src/event/ngx_event.c
+++ b/src/event/ngx_event.c
@@ -892,6 +892,10 @@
     ngx_conf_t            pcf;
     ngx_event_module_t   *m;
 
+    if (*(void **) conf) {
+        return "is duplicate";
+    }
+
     /* count the number of the event modules and set up their indices */
 
     ngx_event_max_module = 0;