`multiproduct.batch` was not defined as an entry point for the `bloodhound_multiproduct` plugin, so it was being discovered as a single-file plugin. Refs #596.

This is similar to the issue resolved in #582.

git-svn-id: https://svn.apache.org/repos/asf/bloodhound/trunk@1513214 13f79535-47bb-0310-9956-ffa450edef68