Insure that Drsh will use backend_invoke() for site aliases where ssh-options are declared, even if remote-host is localhost.
Introduce '#check-local', and require this to be set before redirecting 'remote-host' to the local system. Helps folks using Vagrant.
Merge branch 'backend-invoke-vagrant' of https://github.com/greg-1-anderson/drush into greg-1-anderson-backend-invoke-vagrant