====== qsort ======
  * arrrg _r verze: http://sourceware.org/ml/libc-alpha/2008-12/msg00003.html
  * qsort_r: Linux potrebuje pro glibc -D_GNU_SOURCE
  * reentrantni qsort potrebuje [[github>flightaware/speedtables]]
  * viz take [[github>swenson/sort]]