- critical bug fixed in NCicSubstitution.lift:

- critical bug fixed in NCicSubstitution.lift:
  (0,Irl 0) was lifted to (1,Irl 0)
  but later on NCicTypechecker.check_metasenv_consistency assumes the
  invariant that the currenct context has length (m+n) if the metavariable
  is (m,Irl n). But this invariant is false in the case (m, Irl 0) when m > 0.
- in NCicRefiner there was one line to normalize (m,Irl 0) and (m,Ctx []) to
  (0,...). Is it still required after the first patch to the kernel? I suspect
  no, thus I put an assert false to check.