Make: Don't mess with Vagrant's environment.

The 1.5.x version doesn't like when we override the environment. It
already has support for running within Bundler without the hacky stuff.
Ruby: Be more explicit with the Ruby version.

On many Linux distros, 1.9.x is still the default. Force Bundler to warn
if we are running on anything not compatible with 2.1.0.

Does this work for 2.2.0? I guess not.
Vagrant: Tweak the configuration to use the recommened syntax.

No functional changes.
Provisioning: Since Vagrant 1.5, host names must match.

As of Vagrant 1.5, the machine name (taken from Vagrantfile) is set as
default limit to ensure that `vagrant provision` steps only affect the
expected machine. As a result, the inventory file must reflect the
machine name from the Vagrantfile.
Merge pull request #2 from RogueDudes/vagrant-15-ubuntu-13.10_x64

Vagrant 1.5 & Ubuntu 13.10 (x64)