• added IO::AIO::fadvise and IO::AIO::sendfile.
  
• (libeio) replaced quicksort+insertion sort by a tuned radix
  sort + insertion sort, resulting in comparable runtime (usually
  faster) to the old version, but without any ill side effects on
  degenerated (for quicksort) data.
  
• (libeio) correctly sort dirs by inodes if we have perfect type
  knowledge and DIRS_FIRST is used.
  
• (libeio) internally the wrong DT_* constants were used, but no
  known system has differing EIODT/DT_ values, so not an issue.
  
• removed a (harmless) assert that was left over on the code
  but should not have been.
  
• use more correct types (change IO length from IV to VAL64,
  which makes a difference on systems without 64 bit perls).