Make sure to use datasets transactionally (JENA-1486)
Make sure to use datasets transactionally (JENA-1486)

textindexer did not use datasets transactionally which could fail for
dataset implementations that require transactional usage.  And it is
safer to always use transactions where provided anyway.

This closes #360

apache/jena,apache/jena,apache/jena,apache/jena,apache/jena,apache/jena,apache/jena,apache/jena