Document the policies on binary compatibility more clearly, that:
ICU C and Java API that is marked stable in 3.0 is binary compatible from 3.0
We provide a way to let people check whether they are using only stable API in
ICU4C 3.0 and later; and document that method clearly (In 3.2 we will provide a
way to let people check in Java.)
We make no promises for non-stable API, or API before 3.0.