AthenaKernel, etc: Rename IMetaDataSvc to IAthMetaDataSvc.
To avoid conflicts with a different interface of the same name in Gaudi.
This was an ODR violation. Most of the time, things ended up working correctly, but this was causing a failure in a test of POOLRootAccess.
In principle, the same problem exists with MetaDataSvc itself, for which there is another class of the same name in GaudiSvc. However, renaming that is a much bigger lift, and it has not been observed to cause any problems in practice.
See ATEAM-994.