Scalar PA performance

[Kasper Nielsen]

The performance of the scalar versions of ParallelArray has been discussed
a couple of times on the concurrency interest list. Here are some
pointers.

http://cs.oswego.edu/pipermail/concurrency-interest/2008-January/004899.html
http://cs.oswego.edu/pipermail/concurrency-interest/2007-August/004314.html

Short version: Often 4X faster sometimes up to 16X.

Cheers
 Kasper