mxcl/homebrew — pull request #8073 by bsdf (2011-10-11 19:09:05+00:00)
Title: fix for Formula.installed_prefix

installed_prefix points to the latest available formula version which may or may not exist; it is therefore broken. for example:

```
> brew update
> brew outdated
git node ruby zsh # outdated packages...
> cd `brew --prefix git`
folder does not exist
```

this fix creates a symlink ".current" in HOMEBREW_CELLAR+@name which points to the installed version