Use existing() for ensuring that the importer in question actually exists in DB or in code. Plus one minor cleanup in switch statement.

  scheduled tasks than 'import' and 'expire'.

This is a preemptory step to enable cleaner result handling and prepare the ground for Batch API use.

Don't log to watchdog when starting cron run.

Go back to scheduling 10 feeds per iteration. Breaks tests otherwise. Needs to be adjusted in extra step.