Fix printf warnings

I found these warnings on clang.
Clang recommend to use "zu" for size_t, but I changed to "lu" because MSVC does not support "z" length prefix introduced in C99.

http://msdn.microsoft.com/en-us/library/vstudio/tcxf1dw6.aspx
> The hh, j, z, and t length prefixes are not supported.