Return a bool from is_new(), not an int.
  Comment updates.
  New function file_to_pipe().

  This runs a command, sending it input from the given file.

  (We use this for sending email, via a pipe to sendmail.)
  When calling the user-filter read in a large buffer.
  Use the new CFile::file_to_pipe for sending mail.
  formatting changes only.
  Added new primitive: maildirs_matching()

  This returns a table of maildirs matching a given pattern.

  Closes #37.
  Demonstrate maildirs_matching()
  Don't call imapsync unless it is installed.
  If CLua::execute() fails log the message in debug builds.
  Log CFile::file_to_pipe arguments in debug builds.

  I think this might be useful.