cookbook: Make example code C90 compliant

Modified all cookbook example code to prevent ISO C90 compliance
warnings occurring during compilation.

doc/cookbook/examples/events-buttons-lasso.c

@@ -115,13 +115,13 @@ int
 main (int   argc,
       char *argv[])
 {
-  /* seed random number generator */
-  srand ((unsigned int) time (NULL));
-
   Lasso *lasso = g_new0 (Lasso, 1);
 
   ClutterActor *stage;
 
+  /* seed random number generator */
+  srand ((unsigned int) time (NULL));
+
   clutter_init (&argc, &argv);
 
   stage = clutter_stage_get_default ();