The exception handling only cleanly handles non-class raises - any class exceptions are treated as being internal errors and reported like so:

```
Error: CompilerSelectionError
Please report this bug:
    https://github.com/mxcl/homebrew/wiki/troubleshooting
/usr/local/Library/Homebrew/compilers.rb:64:in `compiler'
/usr/local/Library/Homebrew/build.rb:119:in `install'
/usr/local/Library/Homebrew/build.rb:43:in `main'
/usr/local/Library/Homebrew/build.rb:12
/usr/local/Library/Formula/emacs.rb:107
```