Implement bug #4397 : Fast priority changing. Useful in itself but also needed for next fix.
Reinstate priority on simple mode
Generics
More generics.
Document the tree better
Simpler clearer shorter generics, and get rid of some casts.
Missing file
Rename
Group requests by ClientRequestSchedulerGroup rather than ClientRequester, hence a site insert is a single group (even though PutHandler is ako ClientRequester). Fixes changing priority of site inserts and also makes them compete equally on the global queue with e.g. ordinary inserts.
Fix problems introduced by generics changes (arrays)
Fix NPE