4.5 backports

Backporting 
 - https://hibernate.atlassian.net/browse/HSEARCH-1725
 - https://hibernate.atlassian.net/browse/HSEARCH-1735

to branch 4.5

Relevant differences with master:
 - no changes to LuceneBackendQueueTask
 - to not affect the ErrorBuilder API the ChangeSet class is also able to produce a List rather than an Iterator, so that minimizes changes of 
 - JDK6: no diamond operator, no underscores in constants for separators in numbers, no usage of Collections.emtpyIterator