Merge lp://qastaging/~apinheiro/unity/Bug739689 into lp://qastaging/unity

From the comment I added on the code:

 * Normally not all the accessible objects on the hierarchy are
 * available from the beginning, and they are being created by demand
 * due the request on the AT (ie: orca) side
 *
 * It usually follows a top-down approach. Top objects emits a signal
 * of interest, so AT apps get interest on it, and request their
 * children. One example is the signal "window::activate". AT receives
 * a signal meaning that a top level object is activated, so request
 * their children (and gran-children).
 *
 * Due technical reasons, right now it is hard to find a suitable way
 * to emit the signal "activate" on the BaseWindow. That means that
 * objects on the bottom of the hierarchy are not created, so Orca
 * doesn't react to changes on sections like the Launcher.
 *
 * So in order to prevent that, we make a manual exploration of the
 * hierarchy in order to ensure that those objects are there.

NOTE: this should be a temporal solution, until we get a proper way to notify that top-level windows are being activated.