Improve performance of -profile by factor of 10

[Sean Kelly]

On Mar 22, 2013, at 3:39 PM, Walter Bright <newshound2 at digitalmars.com> wrote:

> http://d.puremagic.com/issues/show_bug.cgi?id=9787
> 
> This can be a fun little project, with a nice payoff. Any takers?

Bonus points if the code is made multithread capable.  When I was thinking about this before, the correct approach seemed to be tracking profile data on a per-thread basis and then merging results into final on thread termination.