pass slices by reference to .query(); pass stderr by reference to writeln!()

I *think* this is the rust change that makes this necessary:

commit b825b3496aff1ed784f7a7ca935245208b95aabb
Merge: dd5ce5a c287afb
Author: bors <bors@rust-lang.org>
Date:   Thu Nov 20 10:01:42 2014 +0000

    auto merge of #18638 : aturon/rust/as_slice_dst, r=japaric

    This PR changes `AsSlice` to work on unsized types, and changes the
    `impl` for `&[T]` to `[T]`. ...