Adds :update_index option to `save' -- passing a false value will prevent `update_index' from
being called after the object is persisted.  The `create_needs_index?' and `update_needs_index?'
methods, however, will not be overridden when they return false.
Merge pull request #433 from dchandekstark/update-index-option

Adds :update_index option to `save'