Minimal MIME for MIME/PEM

There is already an X.400 body part type for PEM, registered in the NIST OIW
agreements.  Its syntax is just an octet string, which is assumed to contain
one PEM (1421) message.  This syntax can be refined if needed, of course.
The OID is:
{ iso(1) identified-org(3) oiw(14) mhsig(6) body-part-types(1) pem(0) }

/ Rich