Port to changed VBO API -- hook_views_bulk_operations_object_info()

Over at #362534: hook_object_info(), VBO renamed its hook from hook_object_info() to hook_views_bulk_operations_object_info() to prevent namespace troubles. That's all well and good, but it means that modules like signup are now in something of a bind. While the world upgrades to 6.x-1.x-dev after views_bulk_operations.module revision 1.29.2.9.2.39 and/or VBO 6.x-1.4, things aren't going to work unless we provide both functions.