- Improvements in ConfigurableUser:
    - Allow dependency between named ConfigurableUser instances.
      The entry in __used_configurables__ can be a tuple where the first element
      is the class (or class name) and the second element is the instance name.
      If the instance name is equivalent to False (None, "", etc.), the name of
      the instance is obtained through the method self._instanceName() that, by
      default, returns "<userclass>_<class>", but can be overridden.
    - Added a method to get a used instance by name: self.getUsedInstance().
  - Minor fix in Configurable: allow to instantiate it passing the name as a
    keyword argument (it was failing if the instance already existed).


git-svn-id: svn+ssh://svn.cern.ch/reps/gaudi/Gaudi/trunk@6128 53ecefc3-a64d-0410-9bdf-b8581fa3287e