Fix the copy in gf_generic

  deleted:    pytriqs/base/gf/local/common.pyx
  modified:   pytriqs/base/gf/local/gf_generic.py
  modified:   pytriqs/base/gf/local/gf_generic.pyx
  modified:   pytriqs/base/gf/local/gf_imfreq.py
  modified:   pytriqs/base/gf/local/gf_imtime.py
  modified:   pytriqs/base/gf/local/imfreq.pyx