tal_count() is used where there's a type, even if it's char or u8, and
tal_bytelen() is going to replace tal_len() for clarity: it's only needed
where a pointer is void.
We shim tal_bytelen() for now.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It's just a sha256_double, but importantly when we convert it to a
string (in type_to_string, which is used in logging) we use
bitcoin_txid_to_hex() so it's reversed as people expect.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>