Fix format specifiers that do not match the argument types

[jamesjer]

In check.h.in, %x is not safe to use with pointers, since it specifies an int-sized value but a pointer is passed in. On some platforms, int is 32 bits and void * is 64 bits.

In check_pack.c, note that t is a length modifier, not a conversion specifier. It must be followed by either d or u; d seems appropriate in this case.

The other changes are fairly obvious mismatches between the argument type and conversion specifier.

[jamesjer]

This commit fixes #270

[brarcher]

Thanks for the fixes!