[v3] more consistent api testing

[Paolo Carlini]

Hi Benjamin,

> Also, synopsis checking is done to sanity check that declarations are 
> correct. Surprisingly, <locale>, <unordered_map>, and <unordered_set> 
> are xfailed.

I'm going to look a bit into the issue myself, but can you detail a bit 
what's going wrong with <locale>??

As regards the unordered containers, the issue coming from the 
additional template parameter is in fact well know (are there any 
other?): as apparent also from some of Matt' comments, he wanted to add 
some additional flexibility, along the lines paved by Ami. Time ago, I 
mentioned on the list that the additional parameter would cause strict 
conformance problems (and we avoided such exact problems while recentlt 
reworking shared_ptr), now probably it's time to rediscuss the thing: 
shall we avoid it, by forwarding from conforming classes to the flexible 
ones? The latter would be uglified but still available, similarly to 
shared_ptr.

Paolo.