Implemented bzip2 formula

Implementation of bzip2 formula including tests.  Passes audit and works on Mac OSX 10.9.4 with latest brew.
This call to File.path seems to be failing on mountain lion:

```
undefined method `path' for File:Class
/usr/local/Library/Taps/homebrew/homebrew-dupes/bzip2.rb:17:in `test'
```

I will figure out an alternative and then reopen the PR.