Update of the Lucene libraries to version 2.9.3. Addition of an attribute for field definitions in the mapping file to make this field unique in the resulting index.

The Lucene library dependency has been updated to version 2.9.3. Thus, some classes had to be rewritten using the new Lucene Token API. Not all classes have been adapted to the new API, however, so that the component is not yet Lucene 3.x compliant.

Lucas creates multiple Field instances for each field declared in the mapping file which is to be stored as well as indexed. This is done even when not necessary. As this may collide with a unique-key property (e.g. in Solr) a new attribute "unique" has been added to the field element of the mapping file. If the value of this attribute is set to "true" and there is only one declaration for this field name in the mapping file, there will be created only one field instance.

This addition has been added to the project's docbook (along with quite some spelling corrections, a few reformulations and corrections to the examples).