lightningd/commit_tx: support for printing out actual tx fees.

This was included in the lightningnetwork/lightning-rfc#105 update
to the test vectors, and it's a good idea.  Takes a bit of work to
calculate (particularly, being aware of rounding issues).

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

lightningd/test/run-commit_tx.c

@@ -5,6 +5,7 @@
 static bool print_superverbose;
 #define SUPERVERBOSE(...)					\
 	do { if (print_superverbose) printf(__VA_ARGS__); } while(0)
+#define PRINT_ACTUAL_FEE
 #include "../commit_tx.c"
 #include "../htlc_tx.c"
 #include <bitcoin/preimage.h>
@@ -15,6 +16,9 @@ static bool print_superverbose;
 #include <ccan/str/hex/hex.h>
 #include <type_to_string.h>
 
+/* Turn this on to brute-force fee values */
+/*#define DEBUG */
+
 static struct sha256 sha256_from_hex(const char *hex)
 {
 	struct sha256 sha256;