Fix some issues in GF

  modified:   pytriqs/base/gf/local/imtime.pxd
  modified:   pytriqs/base/gf/local/mesh_imtime.pyx
  modified:   triqs/gf/imfreq.hpp
  modified:   triqs/gf/local/tail.hpp
  modified:   triqs/gf/test/gfv2.output
  modified:   triqs/gf/tools.hpp