Fixes #299. The linkage exception is now catched.
Learner similar and classify optimisation
Conflicts:
	src/main/java/com/jaeksoft/searchlib/index/IndexConfig.java
	src/main/java/com/jaeksoft/searchlib/index/IndexSingle.java
	src/main/java/com/jaeksoft/searchlib/index/ReaderInterface.java
	src/main/java/com/jaeksoft/searchlib/index/ReaderLocal.java
Merge pull request #302 from emmanuel-keller/master

Improvement and bug fixes