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
* Executed records are pushed onto the undo stack. Records that are undone are
 * popped off the undo stack and pushed onto the redo stack. Records that are
 * redone are popped off the redo stack and pushed back onto the undo stack.
 * Thus, the most recently executed (or redone) record is at the top of the undo
 * stack, and the most recently redone record is at the top of the redo stack.
 * <p>
 * The record stack imposes a limit on the undo stack. When the undo stack grows
 * beyond this limit, the oldest record is flushed.
 * 
 * <h3>Theory of Operation</h3>
 * 
 * The record mechanism relies on accurate implementation of each record.
 * Records change the state of the model, and rely on accurate model state
 * transitions so that undo and redo can be done The following rules must hold:
 * <p>
 * <ul>
 * <li>The execution of a record transitions the model from one state, called
 * the <em>initial</em> state, to another state, called the <em>final</em>
 * state. Think of a model state as a snapshot of the model. Every change of
 * state is done by a record. If the model starts in state S0, then record C1
 * will have S0 as its initial state. ActivityRecord C1 moves the model into
 * state S1, the final state of record C1. A later record C2 will move the model
 * into a new state, S2, and so on.</li>
 * 
 * <li>Both the initial and final states must be <em>valid</em> model states.
 * A valid state is one that satisfies all the semantic constraints of the
 * model. (For example that if an element has a value for property P, then P is
 * a property defined on that element.) Therefore, the record should assume that
 * the model starts out in a valid form, and must leave the model in a valid
 * form.</li>