#988210 by plach and ericschaefer: Refactored the publishing and unpublishing...

#988210 by plach and ericschaefer: Refactored the publishing and unpublishing code in hook_cron() out into separate functions

This refactoring is a preparation step for #988210:

- created _scheduler_publish() and _scheduler_unpublish()
- changed the code so that it would first gather an array of nids out of the query and then iterate over that array instead of iterating directly over the query result