bug#10460: 24.0.92; css-mode sexp movement

[Tom Tromey]

Leo> In a css-mode buffer with the following text:
Leo> a {
Leo>     color: red;
Leo> }
Leo>
Leo> @

Leo> Leave point right behind @ and hit C-M-b, point moved to the opening
Leo> '{'. Is this correct behaviour?

When I do this, point moves to the "a".  This seems clearly wrong to me
-- I think point should be left at the "{".

It seems like a bug in SMIE, in that this ends up calling
(smie-backward-sexp 'halfsexp), which does the wrong thing.

Tom