[Bug libstdc++/52114] SFINAE out the rvalue iostream operators to give better error messages

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52114

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-04 
20:39:58 UTC ---
(PS: Daniel tweaked tuple_cat the same way)