We need to fallback to 'add user script' if 'add machine script' is not available,
otherwise upgrades from 2.2 to 3.0 break. In 2.2, people use 'add user script' to
add machine accounts.
moving this to docs since it wil be a no fix I think and
just documented behavior in the release notes
added comment in the release note about the change in behavior.
Clasing as a nofix.
originally reported against 3.0alpha23. Bugzilla spring cleaning.