update for xcode 5.1.1

- clang 3.4 on default Os X.
- automatically in C++14 mode.
- a little fix in clef (var >> ...) because of an apparent bug in auto
  detection in clang.
magic : redirect std::cout to python sys.out.write

- for all functions, except when GIL option (not implemented) is here
  we use a triqs::py_stream, which redirect the stream
  to python sys.write
- so that a simple C++ code with a std::cout
  print its output in the notebook...
- NB : it only works for the code within the cell.
  If it calls another function on the lib which uses cout,
  print is not redirected.
  Designed for simple tests....
- cerr not (yet) redirected. (useful ?).