Make smemeq return unsigned, not bool.

bool is dangerous in a time-safe context, because C compilers might
insert a control flow divergence to implement the implicit
normalisation of nonzero integers to 1 when you assign to a bool.
Everywhere else time-safe, I avoid using it; but smemeq has been an
exception until now, because the response to smemeq returning failure
was to do an obvious protocol-level divergence _anyway_ (like
disconnecting due to MAC mismatch).

But I'm about to want to use smemeq in a context where I use the
result _subtly_ and don't want to give away what it is, so now it's
time to get rid of that bool and have smemeq return unsigned.

misc.h

@@ -207,9 +207,9 @@ void smemclr(void *b, size_t len);
 /* Compare two fixed-length chunks of memory for equality, without
  * data-dependent control flow (so an attacker with a very accurate
  * stopwatch can't try to guess where the first mismatching byte was).
- * Returns false for mismatch or true for equality (unlike memcmp),
- * hinted at by the 'eq' in the name. */
-bool smemeq(const void *av, const void *bv, size_t len);
+ * Returns 0 for mismatch or 1 for equality (unlike memcmp), hinted at
+ * by the 'eq' in the name. */
+unsigned smemeq(const void *av, const void *bv, size_t len);
 
 /* Encode a single UTF-8 character. Assumes that illegal characters
  * (such as things in the surrogate range, or > 0x10FFFF) have already

utils/smemeq.c

@@ -8,7 +8,7 @@
 #include "defs.h"
 #include "misc.h"
 
-bool smemeq(const void *av, const void *bv, size_t len)
+unsigned smemeq(const void *av, const void *bv, size_t len)
 {
     const unsigned char *a = (const unsigned char *)av;
     const unsigned char *b = (const unsigned char *)bv;