Item12919: trying to improve performance of bulk operations (e.g. trashing 100+ images generated by Motion)

Item12726: don't auto-focus the search field in the attachments list 

also:
- don't use DEBUG as it clashes with Assert.pm
- catch server errors messages properly in ajax calls



git-svn-id: http://svn.foswiki.org/trunk@17714 0b4bb1d4-4e5a-0410-9cc4-b2b747904278