Code to use the new VELO error parametrisation
Back-ported from !431 (merged) on 2017-patches
@masmith FYI. The easiest was to copy the two files from the 2017-patches
releases, and undo the Gaudi::Property
modernisation that is not supported on 2016-patches
Please check that it looks OK, then I'll cherry-pick also to reco15-patches
. Is there a way to test this in Brunel?