Merge pull request #562 in ZP/z-push from bugfix/ZP-1240-html-bodies-should-not-be-truncated to develop

* commit '4b293f5e':
  ZP-1240 Also HTML-trucate bodies from IMAP.
  ZP-1240 HTML safe truncate streams containing HTML data.
  ZP-1240 Add HTML safe truncation options to stream wrappers.
  ZP-1240 Add parameter $htmlsafe (default false) to Utils::Utf8_truncate().