DEBUG: pools: apply poisonning on every allocated pool

Till now, when memory poisonning was enabled, it used to be done only
after a calloc(). But sometimes it's not enough to detect unexpected
sharing, so let's ensure that we now poison every allocation once it's
in place. Note that enabling poisonning significantly hurts performance
(it can typically half the overall performance).
MINOR: samples: add the word converter.

word(<index>,<delimiters>)
  Extracts the nth word considering given delimiters from an input string.
  Indexes start at 1 and delimiters are a string formatted list of chars.