Added another nested level of includes.

examples/c/cfg_includes/book4.cfg

@@ -5,4 +5,5 @@
   qty    = 5;
   list  = (1,2,3,);
   array = [1,2,3,4,5,6,];
+  @include "cfg_includes/cfg_subincludes/*.cfg"
 },

examples/c/cfg_includes/cfg_subincludes/extra1.cfg

+extra1 = "bar";

examples/c/cfg_includes/cfg_subincludes/extra2.cfg

+extra2 = 12345;