Fix for http://www.smarty.net/docs/en/language.modifier.default.tpl

 http://www.smarty.net/docs/en/language.modifier.default.tpl
-This is the default value to output if the variable is empty.
+This is the default value to output if the variable is unset or an empty string

+It does not work for 0 (0 as an integer)/FALSE values as 
http://php.net/manual/en/function.empty.php

+Solution to overwrite
http://www.smarty.net/forums/viewtopic.php?p=88776#88776
