Provides the ability to have simultaneous threaded mailing jobs for a single mailing.

Currently CiviMail will send emails out one at a time, one job at a time. This process limits CiviCRM's ability to scale to large mailings 250K and more. Our patch takes a mailing and generates multiple sub jobs. Each sub job is launched each time the mail cron is triggered and the sub jobs can run simultaneously. This allows you send out your mail faster by processing the mail in multiple instances.

The patch that we will be submitting contains:

1) The logic to split the job in to sub jobs
2) The enhancements to the cron job to pick up a new sub job
3) Changes to the database schema
4) A new smarty template for email reports to handle the sub job results

It is our recommendation that we add this feature to core and set the default number of simultaneous threads to 1 and enable a new setting in the CiviMail configuration page to allow the user to change the number of simultaneous threads. This way users can determine if they want to enable this feature and it wil not break any current configurations.