Fix some obvious bugs in the PKCS#7 library handling. It didn't try to

Fix some obvious bugs in the PKCS#7 library handling. It didn't try to
find the right RecipientInfo based on the recipient certificate (so would
fail a lot of the time) and fixup cipher structures to correctly (maybe)
modify the AlgorithmIdentifiers.  Largely untested at present... this will be
fixed in due course. Well the stuff was broken to begin with so if its broken
now then you haven't lost anything :-)