* ASORT_SWAP(i,j) swap i-th and j-th element (default: assume _ELT
* is an l-value and swap just the keys)
* ASORT_THRESHOLD threshold for switching between quicksort and insertsort
* ASORT_EXTRA_ARGS extra arguments for the sort function (they are always
* visible in all the macros supplied above), starts with comma
*
* ASORT_SWAP(i,j) swap i-th and j-th element (default: assume _ELT
* is an l-value and swap just the keys)
* ASORT_THRESHOLD threshold for switching between quicksort and insertsort
* ASORT_EXTRA_ARGS extra arguments for the sort function (they are always
* visible in all the macros supplied above), starts with comma
*