Define Parallel Plotting

[codinghorror]

@aaronabrown

Plotting has 4 phases.

1. generate lots of info very CPU heavy.
2. combine them down into the tables. very RAM heavy
3. compress them down into the final information. very disk I/O heavy (this is what the -2 second temp directory is for)
4. copy the plot to the final destination.

Current wisdom on 1.1.2 is that you only need 128 buckets and 3400MB of RAM to make sure the work is done with uniform sort and never fails back to quicksort.

This is a fantastic concise summary, just wanted to combine it with the graph from my other topic.