feeds_schedule index mismatch after feeds_update_6008

Hi,

Following update from 6.x-1.0-alpha11 to 6.x-1.0-alpha12 module Schema reports an index mismatch in feeds_schedule table.

In fact, function feeds_update_6008() operates a db_change_field() to rename field last_scheduled_time into last_executed_time. But this field is also an index. Renaming a field which is also an index with db_change_field() requires, as it is stated in the API documentation (http://api.drupal.org/api/function/db_change_field/6), to:

explicitly recreate all indices and primary keys that are using the changed field

Enclosed is the patch implemented as a hook_update.