New C++11 tuple_cat (aka, libstdc++/50159)

[Daniel Krügler]

2011/9/11 Paolo Carlini <paolo.carlini@oracle.com>:
> ehm, forgot the attachments ;)

Thanks Paolo for the quick integration. Let me comment
that I believe that the empty specialization for __or_,

template<>
+    struct __or_<>
+    : public std::true_type
+    { };

should be not be equal to true, but to false,

template<>
+    struct __or_<>
+    : public std::false_type
+    { };

based on the same rationale why any_of returns false
and all_of returns true for the degenerate empty range.

I also think that the std::qualifications of types such as

pair, tuple, array, false_type, true_type

in the added code should better be removed
for consistency, but that is a minor point.

- Daniel