Adapt pade test

Should now be a bit more robust against architectures and compilers.
Also modify slightly the documentation.

  modified:   doc/user_manual/green/block/green_pade.py
  modified:   pytriqs/base/test/pade.output.h5
  modified:   pytriqs/base/test/pade.py
Adapt GF python tests

  modified:   pytriqs/base/test/gf_base_op.output.h5
  modified:   pytriqs/base/test/gf_base_op.py
  modified:   pytriqs/base/test/gf_init.output.h5
  modified:   pytriqs/base/test/gf_init.py