COOK-2197 and COOK-760 - use attributes to determine the selinux state; also some additional enhancements

This pull request is based on j. timmerman's earlier work on COOK-760; that work is now completed. It is also based on an original monkey patch proposed by Sean OMeara here: https://github.com/someara/cookbooks/blob/selinux-monkeys/selinux/libraries/monkeys.rb

This pull request includes some additional enhancements:

- The selinux type can now also be set.
- Triggers automatic relabeling when switching from disabled to other states.
- New recipe to install setroubleshootd.

Update 3/15/2013: I have done more work on this since first opening this push request. There are new LWRPs for SELinux boolean and for SELinux file contexts. In addition, a monkey patch will now automatically call restorecon to fix up the SELinux context for new files and directories. All of it should be idempotent.