Some further tidies in wake of latest location leak

A few things following on from #229 , mainly in `LocationRegistry` API.  @neykov can you cast your eye over this please?
in general, anything that shouldn't be overridden because it is a tiny wrapper around another method, makes sense to be final.  it was haphazard, i think to prevent problems in tests which overrode methods.  have made it more consistent.