The concept was a nice idea to avoid accidental detach() calls
in implicitly shared containers, but it conflicts with a C++11
compatible API for them, with signatures for modifying methods
taking a const_iterator as argument and returning an iterator
(e.g. iterator erase(const_iterator)).
Change-Id: Ia33124bedbd260774a0a66f49aedd84e19c9971b
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>