xtest: lazy load Path::Class::Rule dependency

This will speed-up almost all dzil commands except 'xtest'.
CheckExtraTests: lazy load dependencies

This should speed-up any dzil command except 'release' because
App::Prove will not be loaded.
RunExtraTests: delay loading of App::Prove
Merge pull request #4 from dolmen/fix/lazy-load-deps

Lazy load dependencies