hadley/devtools — pull request #53 by viking (2012-01-26 21:42:08+00:00)
Title: Add as.of.date parameter to install_version()

You can now pass in a date to install_version(). It works by first grabbing the DESCRIPTION file from the latest release (via /web/packages//DESCRIPTION) to check the date, then it uses RCurl to fetch modification times of archived package files. The first version that has an older release date than the specified date gets installed.

Relying on modification times is hacky, but so is this whole function. :) The only alternative I can see is to grab DESCRIPTION files from each archived tarball, unfortunately.