Fix hypo -> cluster navigation in E-correction for SplitPhotons

the navigation from the hypo to the cluster in CaloFutureECorrection (specifically, here) depends on the names of the TES locations in which the containers containing the hypo and the clusters reside (see here)

This MR adds a HACK which gives the containers used in CaloFutureMergedPi0 a dummy name which makes sure that the 'split' cluster is picked up in all cases, instead of, with a small probability, the 'main' unsplit cluster...

Note that this fixes a bug introduced when porting the code to Gaudi::Functional, as at the time the correction is applied, the container is not yet in the event store, where as the pre-functional code first published the container in the event store, and only then started filling the contents. And even then it depended on whether the names of the containers where configured with the word 'SPLIT' (case-insensitive) in them...

Refs updates: Brunel!1065 (merged) Moore!607 (merged)