add rpm 5.4 formula

Copied from https://github.com/mxcl/homebrew/pull/12618:

This formula builds rpm-5.4 - which is very useful for our team, where we target Linux, but develop on OS X.

I had to fix the beecrypt formula so it build 64-bit binaries on 64-bit Lion - somewhere was wrong with the auto-detection magic.

RPM is also only distributed as a source rpm - not a tarball. So I added an RpmDownloadStrategy to handle this. Perhaps extending the CurlDownloadStrategy would have fit in better - but it felt more intrusive.

There is also a minor change to chdir() - it only tries to "cd" into directories - instead of files.

Thanks,
Devin