Homebrew install specific version of formula?

Question

How do I install a specific version of a formula in homebrew? For example, postgresql-8.4.4 instead of the latest 9.0.

Answer 1

I decided, against my better judgment, to create a formula for Maven 3.1.1, which homebrew/versions did not have. To do this:

1. I forked homebrew/versions on github.
2. I symlinked from $(brew --prefix)/Library/Taps to the local working copy of my fork. I'll call this my-homebrew/versions.
3. I tested by specifying the formula as my-homebrew/versions/.
4. I sent a pull request to homebrew/versions for my new formula.

Yay.