ddollar/mason — pull request #1 by technomancy (2012-04-13 00:40:21+00:00)
Title: A bunch of things that should probably be discussed independently

Should have put these in separate topic branches, but this implements

* taking values from the buildpack's bin/release
* updating buildpacks rather than failing when they already exist
* honoring BUILDPACK_URL environment variable
* honoring branches of buildpack URLs
* preserving of the cache

These should probably be discussed independently; happy to rebase some changes out if we decide they're not right.