WL#2552: Parallel Scan in partition handler

Affects: Server-7.0   —   Status: Un-Assigned   —   Priority: Low

The idea here is that scans of large tables that are partitioned should be
performed in parallel. This will increase performance by moving
evaluation of WHERE clause and disk waits to worker threads in the partition

Both full table scans and index scans will be considered.

The partition handler will perform local optimiser functions to decide when
to perform a parallel scan activity.