signing of mail bodies is working now - buuuuut: I changed the behaviour of the ...

signing of mail bodies is working now - buuuuut: I changed the behaviour of the 'signMessage()' function, it now returns *only* the signature part (with a trailing zero).  This is neccessary to avoid confugion at the KMail side: otherwise KMail might try to convert the whole MIME block into quoted printable - of course this is only allowed for the body part but not for the signature part.