Cleanups:
o  Clean up introductory comments.
o  Log messages should show both original and new size of the data. The speed
   should be probably calculated from the former.
o  Buffer sizing in shep-export.
o  Problems with thread stack limit in radix-sorting of arrays.

Users of lib/sorter/array.h which might use radix-sorting:
indexer/chewer.c
indexer/lexfreq.c
indexer/mkgraph.c
indexer/reftexts.c