PO::read_line( resource $f, string $action = 'read' )

	function read_line($f, $action = 'read') {
		static $last_line = '';
		static $use_last_line = false;
		if ('clear' == $action) {
			$last_line = '';
			return true;
		}
		if ('put-back' == $action) {
			$use_last_line = true;
			return true;
		}
		$line = $use_last_line? $last_line : fgets($f);
		$line = ( "\r\n" == substr( $line, -2 ) ) ? rtrim( $line, "\r\n" ) . "\n" : $line;
		$last_line = $line;
		$use_last_line = false;
		return $line;
	}