CiviMailProcessor.php runs into race condition on catchall accounts with a lot of traffic

In 2.1 CiviMailProcessor.php tries to process all mails in the inbox. This might not be possible due to several reasons - for sure it would be time limit on script running time, or other limits (currently have a few thousands mails in the catchall, not sure what exactly breaks, maybe even memory).

In any case much better approach would be to process it chunk by chunk.

See discussion http://forum.civicrm.org/index.php/topic,5997.0.html