Automatically inserts the default_organization into repo URLs if there are no slashes in repo.trimPath().

This allows you to do stuff like sail run sail if your default_organization is set to cdr. If an organization name is in the name passed to parseRepo, it will not prepend the default_organization.

If default_organization = "cdr":

sail run "sail" => ssh@github.com:cdr/sail.git
sail run "deansheather/test" => ssh@github.com:deansheather/test.git
sail run --https "sail" => https://github.com/cdr/sail.git
sail run "https://bitbucket.com/deansheather/test.git" => https://bitbucket.com/deansheather/test.gi

Closes #207.