type_to_string: support sha256_double.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

bitcoin/shadouble.c

@@ -1,5 +1,6 @@
 #include "shadouble.h"
 #include <ccan/mem/mem.h>
+#include <common/type_to_string.h>
 
 void sha256_double(struct sha256_double *shadouble, const void *p, size_t len)
 {
@@ -12,3 +13,4 @@ void sha256_double_done(struct sha256_ctx *shactx, struct sha256_double *res)
 	sha256_done(shactx, &res->sha);
 	sha256(&res->sha, &res->sha, sizeof(res->sha));
 }
+REGISTER_TYPE_TO_HEXSTR(sha256_double);

common/type_to_string.h

@@ -11,6 +11,7 @@ union printable_types {
 	const struct bitcoin_txid *bitcoin_txid;
 	const struct bitcoin_blkid *bitcoin_blkid;
 	const struct sha256 *sha256;
+	const struct sha256_double *sha256_double;
 	const struct ripemd160 *ripemd160;
 	const struct rel_locktime *rel_locktime;
 	const struct abs_locktime *abs_locktime;