math.log() benchmark of first 1 billion int using std.parallelism

[Iov Gherman via Digitalmars-d-learn]

> These multi-threaded benchmarks can be very sensitive to their 
> environment, you should try running it with nice -20 and do 
> multiple passes to get a vague idea of the variability in the 
> result. Also, it's important to minimise the number of other 
> running processes.

I did not use the nice parameter but I always ran them multiple 
times and choose the average time. My system has very few running 
processes, minimalist ArchLinux with Xfce4 so I don't think the 
running processes are affecting in any way my tests.