I have a feeling these will come in handy in other files, but I can't
think of a better place to put them right now. In the meantime:
2) Please name the function __is_null_pointer or __null_pointer_p
or something like that, to make it clear this is a predicate function.
Reading the code where it was used made me think at first that the
function creates and returns a null pointer.
3) This should go in __gnu_cxx, not std. Actually, this should go in
our internal-details namespace, but we haven't invented that name yet.