Using __float128

I try to use __float128 in fvectortest, see !513 (closed). I cannot get ADL to work for >>, abs and sqrt:

In file included from /temp/bernd/DUNE26/dune-common/dune/common/fvector.hh:20:0,
                 from /temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:34:
/temp/bernd/DUNE26/dune-common/dune/common/densevector.hh: In instantiation of ‘typename Dune::FieldTraits< <template-parameter-1-1> >::real_type Dune::fvmeta::absreal(const K&) [with K = __float128; typename Dune::FieldTraits< <template-parameter-1-1> >::real_type = __float128]’:
/temp/bernd/DUNE26/dune-common/dune/common/densevector.hh:603:34:   required from ‘typename Dune::FieldTraits<typename Dune::DenseMatVecTraits<V>::value_type>::real_type Dune::DenseVector<V>::one_norm_real() const [with V = Dune::FieldVector<__float128, 3>; typename Dune::FieldTraits<typename Dune::DenseMatVecTraits<V>::value_type>::real_type = __float128]’
/temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:84:7:   required from ‘FieldVectorMainTestCommons<ft, rt, d>::FieldVectorMainTestCommons() [with ft = __float128; rt = __float128; int d = 3]’
/temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:152:43:   required from ‘FieldVectorMainTest<ft, rt, d, false>::FieldVectorMainTest() [with ft = __float128; rt = __float128; int d = 3]’
/temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:398:5:   required from ‘FieldVectorTest<ft, d, false>::FieldVectorTest() [with ft = __float128; int d = 3]’
/temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:565:36:   required from here
/temp/bernd/DUNE26/dune-common/dune/common/densevector.hh:47:17: error: call of overloaded ‘abs(const __float128&)’ is ambiguous
       return abs(k);
              ~~~^~~
In file included from /usr/include/c++/7/cmath:47:0,
                 from /usr/include/c++/7/complex:44,
                 from /temp/bernd/DUNE26/dune-common/dune/common/test/fvectortest.cc:8:
/usr/include/c++/7/bits/std_abs.h:78:3: note: candidate: constexpr long double std::abs(long double)
   abs(long double __x)
   ^~~
/usr/include/c++/7/bits/std_abs.h:74:3: note: candidate: constexpr float std::abs(float)
   abs(float __x)
   ^~~
/usr/include/c++/7/bits/std_abs.h:70:3: note: candidate: constexpr double std::abs(double)
   abs(double __x)
   ^~~
/usr/include/c++/7/bits/std_abs.h:61:3: note: candidate: long long int std::abs(long long int)
   abs(long long __x) { return __builtin_llabs (__x); }
   ^~~
/usr/include/c++/7/bits/std_abs.h:56:3: note: candidate: long int std::abs(long int)
   abs(long __i) { return __builtin_labs(__i); }
   ^~~

It works only if I place the definitions of >>, abs and sqrt inside namespace std. Which I'm not supposed to do, right?