For S/MIME multipart/signed type the signature is calculated on the fly.

For other detached data forms the stream isn't used after the single pass to
calculate signatures.

For non-detached the data is stored in a memory BIO.

supplied list.

Send ctrls to EVP_PKEY_METHOD during signing of PKCS7 structure so
customisation is possible.

PR: 1071

EVP_PKEY_cmp().

large FD: it's non-blocking mode anyway

only chance for T[ed]4 to get evicted in this module is when its cache
"overlaps" with last 128 bits of key schedule.

prefetch could have been moved closer to Td4 references. Something for
later consideration...