Refactor foreman debian dependencies

This will allow foreman to be installable across more debian distros as
it increases the officially supported ruby packages that foreman depends
on.  The debian project has deprecated the ruby1.9.1 package in testing
(currently jessie), and this will soon propagate to other debian
derivatives.
lib/foreman/export/upstart.rb
Merge pull request #464 from djcp/master

Refactor foreman debian dependencies
Merge pull request #465 from dwilkie/refactor_upstart_export

refactor upstart export
add concurrency example to docs
update docs
0.73.0
update docs
use FOREMAN_ for releases