- Make them work on 64-bit quantities
- clean up use of local pointers to prevent multiple references
  to the pointer (which may have side effects.)

Note that this causes __put_user to produce a warning each time
a pointer is passed as the first argument, since the 64-bit
implementation tries to cast a 32-bit pointer to a 64-bit long.

The fix for this warning waiting for comments from the GCC
community.