mxcl/homebrew — pull request #16164 by vogonistic (2012-11-20 20:20:08+00:00)
Title: External command: brew install-old formula version

This external command makes it easier to install older versions of a
formula by running "brew versions" to find the SHA, creating a
temporary file for it and running "brew install".

This external command depends on the output format from "brew versions"
in order to find the SHA of that version.