WL#2684: Partitioning support in MySQL 5.x, Rolling features

This is a master WL entry for features that might or might not make it into 
the 5.1 release. 
 
In the discussion on 2005-09-28 in Chicago, we agreed that 
the optimizer will catch use in the WHERE clause of both indexed 
and unindexed columns which are also partitioned, and will 
only search the appropriate partition. This is true for '=' 
and non-equal searches, such as '<' and '>' searches. 
This is not rolling, it is flagship for 5.1.