Specifying the condition when an attribute is annotated with UML(obligation=CONDITIONAL)

In most cases, when we have a get method annotated with UML(obligation=CONDITIONAL), the javadoc does not say anything about the condition.
Here I provide a patch in which an @condition tag for javadoc will contain the object of the condition. Martin just has to make the javadoc plugin care about this new tag.

In this patch, there is also a get method that moved from obligation MANDATORY to CONDITIONAL, according to the ISO 19115:2003 standard.