Configure scope on re-evaluation and prioritize CLI scope options
Allow tmux notifier to receive custom types.

This allows the tmux notifier to receive notifications types like
:starting (for instance, when the tests start running).

It will work with the same precedence rules as the already known
types.
Merge pull request #612 from juanibiapina/tmuxnotifier

Allow tmux notifier to receive custom types.
Ensure we load Guard::Plugin as soon as possible. Fix #598.

There seemed to be a conflict with Sass which defined
Sass::Plugin before Guard::Plugin was required…
Merge pull request #611 from IvanUkhov/scope-setup

Configure the scope according to the CLI options on re-evaluation of Guardfile