anchor.diff:  persistent support for various Camel features such as
   Aggregator.
   
  +Current features it provides:
  +
  +* HawtDBAggregationRepository
  +
   *Deprecated*
   
   The http://hawtdb.fusesource.org/[HawtDB] project is being deprecated
   and replaced by https://code.google.com/p/leveldb/[leveldb] as the
   lightweight and embedable key value database. To make using leveldb easy
   there is a https://github.com/fusesource/leveldbjni[leveldbjni] project
  -for that. The Apache ActiveMQ project is planning on using leveldb as
  -their primary file based message store in the future, to replace kahadb.
  +for that.
   
  -There os a camel-leveldb component we recommend to
  -use instead of this.
  +There os a camel-leveldb component we recommend to use instead of this.
   
  -*Issue with HawtDB 1.4 or older*
  +Maven users will need to add the following dependency to their `pom.xml`
  +for this component:
   
  -There is a bug in HawtDB 1.4 or older which means the filestore will not
  -free unused space. That means the file keeps growing. This has been
  -fixed in HawtDB 1.5 which is shipped with Camel 2.5 onwards.
  +[source,xml]
  +----
  +<dependency>
  +  <groupId>org.apache.camel</groupId>
  +  <artifactId>camel-hawtdb</artifactId>
  +  <version>x.x.x</version>
  +  <!-- use the same version as your Camel core version -->
  +</dependency>
  +----
   
  -Current features it provides:
  -
  -* HawtDBAggregationRepository
   
   [[HawtDB-UsingHawtDBAggregationRepository]]
  -Using HawtDBAggregationRepository
  -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  +==== Using HawtDBAggregationRepository
   
   `HawtDBAggregationRepository` is an `AggregationRepository` which on the
   fly persists the aggregated messages. This ensures that you will not
  
positive.code: |`optimisticLocking` |`false` |*Camel 2.12:* To turn on optimistic locking, which often would be needed
  in clustered environments where multiple Camel applications shared the
  same HawtDB based aggregation repository.
  |=======================================================================
  
  The `repositoryName` option must be provided. Then either the
  `persistentFileName` or the `hawtDBFile` must be provided.
  
  [[HawtDB-Whatispreservedwhenpersisting]]
  What is preserved when persisting
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  
  `HawtDBAggregationRepository` will only preserve any `Serializable`
  compatible data types. If a data type is not such a type its dropped and
  
negative.code: send the Exchange when the `maximumRedeliveries` was
  hit.
  
  You can see some examples in the unit tests of camel-hawtdb