Working towards adding attachments to outgoing mails.

  This updates issue #44 by prompting for attachments when sending
 or composing.

  Post-prompt we don't do anything with the entered files.

  TODO:
   * Allow the sendmail primitive to have a table of attachments too.
   * Use the files prompted for.
   * Consolidate email handling in one place.
   * Have a different prompt function: prompt_for_chars( "prompt", "yna");
  Fixed typo in the error prompt.