Controlling S/MIME spec is now v3.2 (RFC 5751)

Changes almost exclusively deal with pkcs7 data.

One new feature to be aware of: a full MIME message can now be wrapped
within a rfc822 part in order to provide verification protection to non-MIME
Headers (e.g. To, From, Cc, Subject).  According to spec, it is up to
MUA to determine how to merge these "inner" headers with the "outer"
headers for purposes of display.  Think we are fine for now - our rfc822
MIME Viewer already displays these basic headers at the top of a rfc822
block, which would be contained within the S/MIME verification box.  We
only guarantee validity of data within that box so that is consistent
with this display.