Add inspection for (probably) undefined variables

[mesour]

Try more variants in fiddle:

{foreach ...}
    {var $level = 0}
{/foreach}

{$level} <= probably undefined variable

{block ...}
    {var $level = 0}
{/block}

{$level} <= undefined variable? todo: check it

{define ...}
    {var $level = 0}
{/define}

{$level} <= undefined variable