indent_test: reduce stack usage for preceding NEWLINEs

In the cases where we allow preceding newlines (Statementlist Open Close)
we current use one parse-stack from for each newline.  While there are
unlikely to be many, this is inelegant.
Change the right-recursive form to use a left-recursive Newlines rule
that absorbs one or more NEWLINEs using at most 2 stack frames.

Signed-off-by: NeilBrown <neil@brown.name>