added a __nonzero__ method to the ListBulker

This is needed to make sure __del__ in ES can detect left over bulk data.
Added 'routing' parameter to ElasticSearchModel's save method

This commit fixes #243
Merge pull request #241 from jukart/es_del_fix

added a __nonzero__ method to the ListBulker
Merge remote-tracking branch 'upstream/master'