API for data only replication #685.
Conflicts:
	src/main/java/com/jaeksoft/searchlib/Client.java
	src/main/java/com/jaeksoft/searchlib/index/IndexSingle.java
	src/main/java/com/jaeksoft/searchlib/index/WriterInterface.java
Merge pull request #688 from emmanuel-keller/master

API for data only replication #685.