OAK-1406: Background operations block writes

- better decouple background write from local commits

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1573517 13f79535-47bb-0310-9956-ffa450edef68
OAK-1479: Failing test for MergeSortedIterators

The IllegalStateException is expected. Client code was wrong. See fix in OAK-1233.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1573520 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of http://git.apache.org/jackrabbit-oak into oak-1475a
OAK-1475 - fixed SolrServerConfiguration and oak-solr-core setup