Install lyx2lyx/lyx_2_2.py.
Update tex2lyx test references

This is needed after c668ebf61. tex2lyx itself was already updated, and I
verified that the new output is correct.
Update version
Fix lyx2lyx warning for tex2lyx files

I would not have thought that reLyX was considered, but not tex2lyx!
Update documented command for running tex2lyx tests.