undefined function simplenews_switch_user()

About that there is a note on the project page:

ccprog's patch is committed in the dev release so you need to apply patch from #256795: Allow simplenews cron to send nodes that anonymous users cannot access to Simplenews to make this work. Otherwise you will got an error about the undefined simplenews_switch_user() function.

If you don't want to apply the mentioned patch to Simplenews you can simply remove the simplenews_switch_user() lines from the simplenews_scheduler_new_edition() function. Anyway, I think we will create a stable release soon that will not contain this if Simplenews doesn't have a stable release for it.