parsergen: track when newline is permitted, and discard if not.

parsergen: track when newline is permitted, and discard if not.

A newline is only permitted (as a recognised symbol) if we are
parsing a non-indented line-like segment.
If we have seen an internal indent since the last line-like start,
newline tokens should be ignored.

Signed-off-by: NeilBrown <neilb@suse.de>