Fixed the type of some ivar access functions. Ivars have type uintptr_t,

Fixed the type of some ivar access functions.  Ivars have type uintptr_t,
not u_long.  On i386's with 64-bit longs, returning u_longs indirectly
in (more than) the space reserved for uintptr_t's tended to corrupt the
previous frame pointer in the stack frame, so it was not easy to debug.
The type mismatches are hidden by the bogus cast in DEVMETHOD().