Clean up cython TailGf class

  modified:   pytriqs/base/gf/local/tail.pxd
  modified:   pytriqs/base/gf/local/tail.pyx
Add python "with" support in archives

  modified:   pytriqs/base/archive/hdf_archive.py
  modified:   pytriqs/base/archive/hdf_archive_basic_layer_h5py.py