function _unlink($resource, $exp_time = null)
	{
		if(isset($exp_time)) {
			if(time() - @filemtime($resource) >= $exp_time) {
				return @unlink($resource);
			}
		} else {
			return @unlink($resource);
		}
	}
function _unlink($resource, $exp_time = null)
	{
		if(isset($exp_time)) {
			if(time() - @filemtime($resource) >= $exp_time) {
				return @unlink($resource);
			}
		} else {
			return @unlink($resource);
		}
	}
function _unlink ( $ resource , $ exp_time = null ) { if ( isset ( $ exp_time ) ) { if ( time ( ) - @ filemtime ( $ resource ) >= $ exp_time ) { return @ unlink ( $ resource ) ; } } else { return @ unlink ( $ resource ) ; } }
unlink a file, possibly using expiration time

@param string $resource
@param integer $exp_time
unlink a file possibly using expiration time