Require and use 'posix/spawn' when running ruby 1.8 without using Foreman.ruby_18? (which is the subject under test).
Fail with an error on Ruby 1.8 when posix-spawn is not present.
Merge pull request #360 from kjwierenga/feature/require-posix-spawn

Feature/require posix spawn
Merge pull request #305 from marclennox/master

Add start-stop-daemon export support with upstart