@Lorraine Chapman

This change potentially changes the order that records are returned from stepped index reads with multiple input keys. Previously the payload was used for ordering, now it is restricted to the keyed portion.

Detail:

Previously the order was determined by the trailing keyed components, the payload memcmp'd and finally any leading keyed components.  This would cause problems if payload fields are removed or added since the ordering would no longer be consistent.  (The previous code also potentially returned data in an undefined order since it was possible for exact matches to access uninitialised data.).

 After this change the order is determined by the trailing keyed components, and then leading keyed components.  If there are exact matches between multiple keys all results will be returned from the first matching keys, before exact matches from the next key.