"error: the type of this value must be known in this context" for `as_ref`

[emk]

With:

$ rustc --version 
rustc 1.15.0-nightly (03bdaade2 2016-11-27)

I get the following error:

error: the type of this value must be known in this context
   --> /home/emk/.cargo/registry/src/github.spider-man.dpdns.org-1ecc6299db9ec823/postgres-0.13.2/src/lib.rs:794:61
    |
794 |                 let get_raw = |i| row.get(i).and_then(|r| r.as_ref().map(|r| &**r));
    |                                                             ^^^^^^

This looks like it's related to 11f1186 and possibly rust-lang/rust#36340.