Prevent occasional hibernate session errors during run-seed.

In grails 2.3.5, I was running into the occasional "No Hibernate Session bound
to thread, and configuration does not allow creation of non-transactional one
here" exception when executing the run-seed task.  By forcing initialization of
the persistenceInterceptor, we can prevent those exceptions.
Merge pull request #5 from ajbrown/master

Prevent occasional hibernate session errors during run-seed.