[PATCH] Add explicit default constructors where required by the standard

[Jonathan Wakely]

On 14 May 2013 10:56, Jonathan Wakely wrote:
> On 14 May 2013 10:45, Evgeniy Stepanov wrote:
>> This must have fallen through the cracks.
>
> It's still in my Git branch at home. I've been too busy to push any
> commits recently, but I haven't forgotten it.
>
>
>> I realized we also need it in the 4_7 branch. Could you backport the
>> change there, too, if it is not too much trouble?
>
> Yes, for such a small, safe change I'm happy to apply it to the 4.7 branch too.

Done.