Revision 1756437

PIVOT-948:  Add an example program that both illustrates how to use data binding
(in this case, "selected item binding" with a ListButton), but that also serves
as a check on the fix for this issue.  Having an unselected item used to cause
the bind mapping not to be called during a "store" operation.  Now it is called
always (if set), and the mapping is responsible for translating between the
unselected state/index and the underlying stored value.