Fix bloody printf specifiers.

In particular, even in code that only runs on x86-64, you can't use
PRIx64 for size_t because, on OS X, one is unsigned long and the other
is unsigned long long and clang whines about the difference.  I guess
you could make a size_t specifier macro, but those are horribly ugly, so
I just used casting.

Anyone want to make a nice (and slow) template-based printf?

Now without bare 'unsigned'.