Checks the {@link #isDirty} state of the field and if it has changed since the last time it was checked,
fires the {@link #dirtychange} event.
function() {
        var me = this,
            isDirty = me.isDirty();
        if (isDirty !== me.wasDirty) {
            me.fireEvent('dirtychange', me, isDirty);
            me.onDirtyChange(isDirty);
            me.wasDirty = isDirty;
        }
    }