Fix + a constant operator in tail

  modified:   triqs/gf/local/tail.hpp
Add possibility to do pure c++ hdf5 based tests

Now one can also do c++ tests which generate an
hdf5 output to be compared.

  modified:   cmake/FindTestCSimple.cmake
  modified:   cmake/run_test_simple.cmake
Deducing value_type in lazy doesn't work on gcc

  modified:   test/triqs/arrays/matmul2.cpp