Make gtest work with libc++.

In C++11 mode, #include <tuple> unconditionally, and 'using' std::tuple and friends into std::tr1. In C++98 mode, libc++ doesn't define tuple<>, so force GTEST_USE_OWN_TR1_TUPLE.

[michael181189, 2013-02-02 22:09:08]

Thanks. Did the trick with apple clang and std=c++11 -stdlib=libc++ which was
broken because gtest looked for tr1/tuple instead of tuple

Michael