Offer nightly builds of master

[nikomatsakis]

Given that we always suggesting to people that they should use the version of rustc found in git, it would be friendly to offer nightly builds. This might also prevent our dist targets from bitrotting. @graydon can confirm but I imagine this is the sort of thing that the transition to buildbot will help with.

[cnd]

I want nightly builds too because my code on Linux where I use rust from master fails (sure) on windows where I don't really want to build rust.

I'm forced now to build because I feel that it's better then write outdated syntax but using nightly will be much better.

• auto-update-able builds will be more better.

[bstrie]

Thirded. Lots of people wind up in the IRC channel asking if there are nightly builds. Hopefully this isn't too hard now that buildbot has been set up.

[lucian1900]

They work particularly well for projects with slow/annoying builds, like PyPy. In fact, PyPy's design would make development almost intractable without nightlies.

[catamorphism]

Nominating for milestone 5 (production-ready)

[pnkfelix]

just-a-bug, not a milestone (once we're in production, the customers won't be using nightly's)

[metajack]

triage bump

[alexcrichton]

Closing in favor of #9876 which is tagged and has a milestone