Fixed problem with edm::Refs from secondary source in RecoTrackAccumulat...

...or

edm::Ref like objects do not work when they come from the secondary source
used by the mixing module. To work around this one must get the container
directly and then use the index in the edm::Ref to find the right item in
the container. This change does this and properly handles copying from the
secondary source to the new edm::Event.
TrajectorySeeds are not handled by this change, since it was unknown if it
would be necessary. If they are needed, the same procedure done for the other
Refs can be done for them.