Bug 148755 Add tthe status to the ActivityStackEvent.
If the the event rollback, the ActivityStackEvent status should be ROLL_BACK.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/activity/ActivityStack.java
* Above we said that a record must leave the model in a valid state. This rule
 * applies only to top-level records. It is expected that the model may be in an
 * intermediate state during part of a compound record. For example, suppose we
 * want to delete an element E that is referenced by three other elements. We
 * would implement this as a compound record. The first three sub-records would
 * remove the references to E. Then, the final sub-record would delete E itself.
 * The initial and final states of the overall compound record are valid, but
 * the states between sub-records are not necessarily valid.
 * <p>
 * As a convenience for the application, the compound record implementation is
 * abstracted into the concept of a <em>transaction</em>. The application
 * simply calls startTrans( ) to start a series of operations to be treated as
 * atomic, and calls commit( ) to complete the series. For convenience,
 * transactions can nest to any depth. Only the outermost transaction shows up
 * as a an undoable or redoable record in the UI.
 * <p>
 * It is important to understand when records execute within a transaction.
 * Records execute during the call to execute( ) on the record stack. That is,
 * whether or not a record is part of a transaction, it executes immediately
 * when added to the record stack. Note that this model differs from other
 * systems, such as GEF, that defers execution of nested records until the
 * compound record itself executes. However, the incremental execution model of
 * this implementation means that the application need not know whether a record
 * is part of a transaction or not, the effect on the model state is identical.
 * This model is important to allow code to work directly with the model,
 * knowing that the model reflects the series of records executed previously.
 * 
 * <h3>Error Handling</h3>
 * 
 * The record stack is a low-level operation primarily responsible for managing