Fix some indices in python gf

  modified:   pytriqs/gf/local/descriptors.py
  modified:   pytriqs/gf/local/gf_generic.py
  modified:   pytriqs/gf/local/tail.pyx
Fix in matrix_stack_view

  modified:   triqs/arrays/matrix_stack_view.hpp
Fix matrix_view_proxy

  modified:   triqs/arrays/matrix_view_proxy.hpp