Implements #710
Conflicts:
	src/main/java/com/jaeksoft/searchlib/index/IndexSingle.java
	src/main/java/com/jaeksoft/searchlib/index/WriterLucene.java
	src/main/java/com/jaeksoft/searchlib/scheduler/task/TaskDeleteQuery.java
Merge pull request #713 from emmanuel-keller/master

Implements #710