ACTION-312: Check on S/MIME normative use of KEM

This is in response to ACTION-312 that I got during last week's call.

I have checked with the chairs of IETF S/MIME. As there are no firm plans 
for a new version of S/MIME right now (the latest is S/MIME v3.1), they 
have also not taken any stance with regards to normative use of Key 
Encapsulation.

Based on this, we may want to start out with having key encapsulation as
OPTIONAL in 1.1.

-- Magnus