Maven pom file for jbpm-jpdl should define jackrabbit-core dependency as optional

jackrabbit-core implementation of JCR should be defined as optional dependency, because any maven based project which doesn't need to use JCR jbpm feature downloads this dependency and also its transitive dependencies.

If you look at http://maven.apache.org/guides/introduction/introduction-to-optional-and-excludes-dependencies.html, there is clear description why use <optional>true</optional> in maven project.

Please fix the jbpm-jpdl pom file.