Rust nightlies get out of sync across platforms

[carllerche]

We are using Rust in production at Tilde. Our product requires shipping builds for OS X & Linux. Given the flux of Rust, we are tracking the nightlies and updating our code as there are breaking changes. However, we have been noticing that the Linux nightlies and the OS X nightlines are not kept in sync. This means that we cannot keep our code base in a state that compiles on the nightlies.

Currently, the OS X nightly installs a build from 10/31/14, but the Linux nightly installs a build from 11/02/14, which are incompatible.

It would be great if builds could be pushed out "atomically" for all platforms.

[alexcrichton]

Closing as a dupe of #14431