memory management barfs 5.005_56+
tvgen.pl
  copy tvcommon.[ch] only if newer
avoid installing .so stuff?
*** SCALING UP
allow treefill/depth updates to be switched off temporarily?
  reduce the need for write locks == parallel insert mode...?
optimized arrays ops: tc_splice(...) !!
perl interface -> separate extension
  REFCNT!
  push/unshift & pop/shift flags
  transient hash-ref indices?
  tied array API & glue
  array: mapkeys / mapvalues?
OPTIMIZE!
tc_delete
  try 2-level rotations?
  try to coalesce nodes before they are completely empty