Implements #710
Conflicts:
	src/main/java/com/jaeksoft/searchlib/index/IndexLucene.java
	src/main/java/com/jaeksoft/searchlib/index/WriterLocal.java
	src/main/java/com/jaeksoft/searchlib/scheduler/task/TaskDeleteQuery.java
	src/main/java/com/jaeksoft/searchlib/webservice/document/DocumentImpl.java
Merge pull request #712 from emmanuel-keller/1.6

Implements #710