bump version to 12.0.0.alpha.0

also include warning about the use of Chef::Version on Chef::VERSION's

people keep stumbling across this bug all the time and i think i
just figured out how some of them are getting the idea...
note on using Gem::Version instead of Chef::Version
fix unit test
fix this right so it doesn't break in chef-13 too
Remove appending :actions and :valid_actions
Merge pull request #1661 from opscode/lcg/chef-12-version-bump

bump version to 12.0.0.alpha.0