Package libpst-docs: Information

- NMU: rebuilt with boost-1.67.0

- a further fix for empty headers instead of the authentic correct ones
  for the very rare case when the first internet header is wrapped
  (thx Carl from upstream, hg commit e4c414ff8fa2)

- rebased onto 0.6.68 ("To: " has become a "known" header in readpst, too).