Use pointers so plan.Clean() works

[shanson7]

Verified locally. Results in a moderate reduction in alloc rate for query nodes.

[Dieterbe]

fix #1799

I must be missing something, but given that a map is basically a by-reference type, copying the plan (and getting a "reference" to the same map) should be harmless. what am i missing?

[shanson7]

We are updating the wrong reference.

As an example:
We start with plan A with A.data at address 0x100 pointing to map at address 0x50
When calling executePlan we copy that plan to plan B with B.data at 0x150 pointing to address 0x50
When calling plan.Run() as a value ref we copy B as plan C with C.data at 0x200 pointing to address 0x50.
We update C.data so 0x200 now points to our dataMap at 0x175. However A.data and B.data both still point to 0x50 (the wrong map).

[Dieterbe]

Ah, I see. I thought we just inserted into the map, but we re-assign to it in plan.Run with p.dataMap = dataMap. d'oh...