Aborting of child threads occurs only if the crawlmaster also aborts #1305
Fix #1316

Conflicts:
	src/main/java/com/jaeksoft/searchlib/cache/FilterCache.java
	src/main/java/com/jaeksoft/searchlib/index/IndexSingle.java
	src/main/java/com/jaeksoft/searchlib/learning/StandardLearner.java
	src/main/java/com/jaeksoft/searchlib/web/controller/runtime/CacheController.java