Unit tests for CMath::qsort(): Trying to sort empty lists with qsort(*T) and qsort(**T)

A bunch of tests:
* for the fixed bug of qsort(*T)
* for the fixed bug of qsort(**T)
* for the fixed bug of qsort_index()
* for the fixed bug of qsort_backward_index()

Fixed qsort(), qsort_index(), parallel_qsort_index(), qsort_backward_index() and parallel_qsort_index().