[Bug libstdc++/51013] complex::{imag,real}() should maintain lvalue-returning extension in C++11

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51013

--- Comment #13 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #8)
> Once we have ref-qualifiers, it should be OK to add the non-const overload
> with an lvalue ref-qualifier, though.

Now we have ref-qualifiers. Do we want to provide the extension in C++11 mode,
or officially say we won't?