Support for Vagrant 1.5

This is last night's work for GH-242, GH-241, GH-191, GH-213 (incomplete) and GH-111, use at your own risk ;-)

### TODO

* [x] Support for Vagrant 1.5's `vagrant share`
* [x] Convert acceptance specs to vagrant-spec
* [x] Backport Action::IsState, Action::HandleBox, Action::Message
* [x] Backport Vagrant < 1.5 functionality and make sure things are working fine across all Vagrant 1.1+ versions.
* [x] Merge GH-245 into master
* [x] Rebase and merge this PR