included.rb in itamae-1.1.15

- old
+ new

@@ -1,7 +1,15 @@
+require 'pathname'
+included_flag_file = Pathname.new("/tmp/included_rb_is_included")
+if included_flag_file.exist? && included_flag_file.read == $$.to_s
+  raise "included.rb should not be included twice."
+else
+  included_flag_file.write($$.to_s)
+end
+
 execute "touch /tmp/included_recipe"