This commit supplements the optimisations of equalities in conjunctions
and disjunctions:
* for conjunctions, the existing optimizations with ranges are extended
with not-equalities and inequalities; these lead to a fast resolution,
the conjunction either being evaluate to a FALSE, or the non-equality
conditions being dropped as superfluous;
* optimisations for disjunctions are added to be applied against ranges,
inequalities and not-equalities; these lead to disjunction either
becoming TRUE or the equality being dropped, either as superfluous or
merged into a range/inequality.

* Fix the bug around wrongly optimizing 'a=2 OR a!=?', which only yields
TRUE for same values in equality and inequality.
* Var renamings, code style adjustments, comments corrections.

- fix a few code comments;
- extend the Equals OR NotEquals optimitsation (a=2 OR a!=5 -> a!=5);
- extend the Equals OR Range optimisation on limits equality (a=2 OR
  2<=a<5 -> 2<=a<5);
- in case an equality is being removed in a conjunction, the rest of
  possible optimisations to test is now skipped.

- s/rmEqual/removeEquals

…als-optimisations