raptor_turtle_writer_quoted_counted_string handles a counted string

(raptor_turtle_writer_contains_newline): Add len param and use it,
drop strlen().

(raptor_turtle_writer_quoted_counted_string): Use len, drop strlen()
and call raptor_turtle_writer_contains_newline with passed in len.

Fixes Issue #0000576
http://bugs.librdf.org/mantis/view.php?id=576