Work again with recent cargo

Cargo seems more useful now, so re-enable this, after fixing a few
things.
Fix sqlite cursor mutability

commit 8e8f61b825deae48f08b7d8023e37e339c15a879
Author: Kang Seonghoon <public+git@mearie.org>
Date:   Thu Jul 31 01:20:04 2014 +0900

    fixes various mutability problems.

    - fixed a mistake that `Database` was accidentally `Send`able.
    - made `Cursor::{reset, clear_bindings, step, step_row,
      get_blob, get_int, get_i64, get_f64, get_text, bind_param,
      bind_params}` receive `&mut self`.
    - made `Database::set_busy_timeout` receive `&mut self`.
      `Database::{prepare, exec}` has been left as is, since it is
      perfectly safe to have multiple cursors. the associated
      thread safety issue is separately handled.

    closes #98, #99, #100, #101 and #103.

Makes many cursor operations explicitly mutable.  Fix the vars used so
this continues to work.