used for rwi ranking.
Main changes:
- introduce a posintext() to access the stored value. This reduces also mem alloc of position array for WordReferenceRow (index access)
- use the positions() array for joined references on multi-word queries if needed (otherwise allow positions() to be null
- adjust assignments and the min() max() and distance() calculation accordingly
Issue was the calculation in AbstractReference with positions.clear() call,
this made distance result always 0 (distance needs min 2 positions) and created concurrency issues.
+ unit test of changes
luccioman