Changed to the C9x draft spelling of the (unsigned) integral type

Changed to the C9x draft spelling of the (unsigned) integral type
suitable for holding object pointers (ptrint_t -> uintptr_t).
Added corresponding signed type (intptr_t).  Changed/added
corresponding non-C9x types for function pointers to match.  Don't
use nonstandard types to implement these types, and don't comment
on them in <machine/types.h>.