[v3 PATCH] Make the default constructors of tuple and pair conditionally explicit.

[Paolo Carlini]

Hi,

+  template <typename _Tp>
+    struct __is_implicitly_default_constructible
+      : public integral_constant<bool,
+                    (__and_<is_default_constructible<_Tp>,
+                            __is_implicitly_default_constructible_safe<_Tp>
+                           >::value)>


Can we follow the terse style already used elsewhere (eg, 
__is_direct_constructible_new_safe) thus directly inherit from __and_ 
and avoid explicit integral_constant? Otherwise patch looks good to me.

Thanks,
Paolo.