Re-apply @stevengj's commit e956b3c36f5fea929d5af8cd17b64682f7.

GitHub won't let me download or recover this commit, even though it's
very much publically visible:

https://github.com/JuliaLang/julia/commit/e956b3c36f5fea929d5af8cd17b64682f7

The easiest way to recover from the accidental forced push of master
seems to be to just re-apply this lost commit and carry on. See

https://groups.google.com/forum/#!topic/julia-dev/RE9k7ips7Dc