'Clean up Caches' deletes in progress batches

My suggestion is to append a 'data' column to the civicrm_batch table rather than store entered data in the civicrm_cache table (which doesn't seem to be appropriate to me as this is 'source' data not a performance caching).

If this approach is OK AND we do decided to use the batch data entry for 4.4 I will do a PR. It seems like the requirement is

• schema change civicrm_batch - add field data, longtext
• upgrade script change - add field data, longtext
• alter CRM_Batch_Page_AJAX to save to the data field not cache
• alter CRM_Batch_Form_Entry to retrieve defaults from data field not cache
• possibly alter CRM_Batch_Form_Entry to set data to NULL when completed (not sure it wouldn't be better to retain in case of probs)
• alter CRM_Batch_Form_Entry not to attempt to delete the cache string