Save loop should include a latest-at view from the beginning of the loop

[jleibs]

In: #3148 we introduced GarbageCollection options that have the ability to protect certain components if they are the latest instance of the component on a particular timeline. This has the nice property that data (in particular early-logged timeless or near-timeless values) don't disappear leaving you with a partial view.

It would be nice to do something similar to this on saving loop so that the saved loop is guaranteed to include all of the data that is relevant to its presentation, even if that data was logged before the loop.