DATAJPA-492 - Altered implementation of findAll(Iterable<ID>) to work around bug in OpenJPA.

Changed the implementation of SimpleJpaRepository.findAll(Iterable<ID>) as OpenJPA still doesn't correctly bind in-clauses by name. This has been originally reported in [0] and marked fixed for 2.3.0 but even an upgrade to this version (coming in a subsequent commit) requires the workaround.

[0] https://issues.apache.org/jira/browse/OPENJPA-2018