[v3 patch] Fix friend declaration so it is visible to name lookup

[Jonathan Wakely]

On 21/08/15 00:03 +0200, Paolo Carlini wrote:
>Hi,
>
>On 08/20/2015 10:21 PM, Jonathan Wakely wrote:
>>Jason pointed out this isn't valid, and is going to fail to compile
>>soon with a fix he's making.
>I seem to remember that at some point we had the exact same issue with 
>some member operator<< and operator>> of <random>.

I don't remember that, but hopefully we won't have any more problems
like this now that Jason is making the front-end diagnose it.