This was paranoia on my part: account_picker does not own acctsSlice, it is passed in from somewhere else. In this case, it comes from model. model does set acctsSlice.oncomplete handler, but not onsplice or onchange. However, during an interim set of changes, I thought I needed to listen to onchange elsewhere.

I would like to see slices support multiple event listeners, but that is a separate discussion, there may be reasons not to do it, and if it is done, will be a larger changeset.

Options for this pull request:

1) Remove the old* stuff since there is not technically a conflict at the moment, and hope that longer range changes to how model and/or event binding for slices are changed before it becomes an issue (which I am interested in pursuing).

2) Change account_picker to just get its own acctsSlice by calling MailAPI.viewAccounts(). settings_main does this already for itself, so there is precedent.

I am leaning towards 2.