The parser now warns about use of mutbl-ref mode, though it's kind
of a lie since this commit doesn't remove support for the mode.
Changed move_val_init to have stage0 and stage1/2 versions, the latter of
which is demoded.
Changed the type that the typechecker expects the move_val_init
intrinsic to have. After this is pushed, I can make a new snapshot,
which will remove the need for the stage0 versions.
