add spark comparison functions

[yma11]

add comparison vector functions for equalto, lessthan, greaterthan, lessthanorequal and greaterthanorequal. NaN value is specially handled.

[PHILO-HE]

Can you add some tests to get infinity involved in the comparison? E.g., compare infinity with Nan. I remember this case is also specially handled.

[yma11]

@PHILO-HE Seems no need update functions internal. Add some tests for Infinity, referring spark doc.

[PHILO-HE]

Vector function has a null behavior by default, which produces null result if any input is null. So I think we can skip the check for null. See VectorFunction.h:

  virtual bool isDefaultNullBehavior() const {
    return true;
  }

Thanks!

[yma11]

Vector function has a null behavior by default, which produces null result if any input is null. So I think we can skip the check for null. See VectorFunction.h:

  virtual bool isDefaultNullBehavior() const {
    return true;
  }

Thanks!

updated.

[PHILO-HE]

LGTM