ESS EncapsulatedContentType

All:

ESS currently includes this definition.

  EncapsulatedContentType ::= CHOICE {
    built-in ...
    external ...
    externalWithSubtype ... }

External is an OID, and it is similar to the content type carried in
signed-data.  We could eliminate the built-in if we assigned OIDs for each
of the few integers that are assigned.  This would simplify the structure.

The externalWithSubtype will not be used often, and the subtype is not
really important in the receipt request context.  It is really used to flag
that automatic processing of the message is necessary.  Therefore, I
propose moving the subtype to a separtae authenticated attribute.

If people accept both of these proposals, then the ESS document should use
the content type attribute defined in the CMS document.

Russ