Added support for Ubuntu 14.04

I've added (and tested) support for the new LTS version of Ubuntu: 14.04.

This pull request is meant for discussion. I've not rebased the commits so far to make it easier to discuss. While the package installation support just introduces a minimal change and should be ok, the change in the source installation doesn't looks good. While it works, it is obvious that the platform number check at this place can lead to "spaghetti code" in future. Wouldn't it being better to have some "_feature_check.rb" on top of "source.rb" which checks the platform and sets some flags like "need_lib_event_patch" and so on? In the recipes these variables could be checked then instead of checking the platform again and again. Of course I'm open to different ideas.

Also I would check Ubuntu 14.10 too before merging the pull request. It is likely that it can be added without many chances, but haven't tested it so far. At least the `hhvm` github page mentions 14.10 already.

Thorsten