FELIX-4268 Duplicated name errors always happen when there are 2 factories with the same name

* Generating a name always produce a unique name
* When name is provided by the instance, only check uniqueness and try appending factory's version if any, then re-check
* Changes NameGenerator interface (no more used for provided name verification)

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1528820 13f79535-47bb-0310-9956-ffa450edef68