CVE-2013-6401: Change hash function, randomize hashes

Thanks to Florian Weimer and Eric Sesterhenn for reporting, reviewing
and testing.
static JSON_INLINE int isinf(double x) { return !isnan(x) && isnan(x - x); }

static JSON_INLINE int isinf(double x) { return !isnan(x) && isnan(x - x); }
