- Fixed operator precedence rules for multiple

- Fixed operator precedence rules for multiple
chains of a single non-associative operator.
I.e. "x - (y - z)" will compile as "x - (y - z)"
and not "x - y - z".  Also works with labels,
i.e. "x - (y - z).label('foo')"
[ticket:1984]
- Single element tuple expressions inside an IN clause
parenthesize correctly, also from [ticket:1984],
added tests for PG
- re-fix again importlater, [ticket:1983]