While this doesn't make, and never made, any sense (pointers should be
stored in a plain, non-object array), we still should continue to
support it for compatibility.
Fix the problem introduced by 97684a9267
by writing "T const&" instead of "const T&" as the latter didn't have
the same meaning when the macro parameter "T" expanded into "U*" as
"const" applied to "U", making this type incompatible with the actual
one.
Also extend the unit test to check for this.
02ffdd16f6