Fixed XMLSummarysvc usage with RootIOAlg

The XMLSummarySvc was not compatible so far with RootIOAlg, mostly because it was not thread safe and relying on incidents which were not all fired, and not in the expected order.
This has now been fixed, based on extra incidents and more information inside the incidents, making the handling of them thread safe.
However, the XMLSummarySvc is still very fragile and would benefit of a complete refactoring, potentially based on the new monitoring machinary now available.

On the way, the unit tests for the XMLSummarysvc have been improved. We now also test for the file status and try to read 2 files, a small one first which is fully read, and a longer one which is partially read.