Improve performance of -profile by factor of 10

[Walter Bright]

On 3/26/2013 4:52 PM, Vladimir Panteleev wrote:
> Even when the overhead of a polling profiler is higher, it has the qualifying
> difference in that the performance overhead does not skew the execution times of
> particular parts of a program as much as an instrumenting profiler. That is,
> while an instrumenting profiler makes some parts of the program much slower than
> others, a polling profiler should make the whole program about equally slower.

I've done a lot of very successful optimization jobs using -profile. Sure, it 
isn't terribly accurate, but it's plenty accurate enough where it matters.