Update to latest rust nightly

The exact version is rustc 0.13.0-dev (0b7b4f075 2014-11-16 22:36:50 +0000) and
the relevant upstream issues are rust-lang/rust#18752 and rust-lang/rust#18976.

Fixes #439.
Merge pull request #440 from aepsil0n/update_nightlies

Update to latest rust nightly