Reviewed FIXME-comments.

Rev: nettle/aes-decrypt-internal.c:1.2
Rev: nettle/aes-encrypt-internal.c:1.2
Rev: nettle/aes-internal.h:1.2
Rev: nettle/arctwo.h:1.2
Rev: nettle/base16-decode.c:1.2
Rev: nettle/base16-encode.c:1.2
Rev: nettle/base16.h:1.2
Rev: nettle/base64.h:1.2
Rev: nettle/bignum-random.c:1.2
Rev: nettle/bignum.c:1.2
Rev: nettle/bignum.h:1.3
Rev: nettle/rsa-sign.c:1.3
Rev: nettle/rsa-verify.c:1.3
Rev: nettle/rsa.c:1.3
Rev: nettle/rsa.h:1.2
Rev: nettle/sexp-transport-format.c:1.2
Rev: nettle/sexp.c:1.2
Rev: nettle/sexp.h:1.2