add support for data federations

The IODataManager will try out all PFNs in the file catalog until one entry is
found, which can be opened.

From: Markus Frank <markus.frank@cern.ch>


git-svn-id: file:///afs/cern.ch/work/b/binet/dev/repos/gaudi-svn-mirror/Gaudi/trunk/GaudiUtils@7367 22b0f739-a4da-4a50-9948-337547c35a65