thread aware malloc

[Ivan Voras]

Niall Douglas wrote:

> I've already ported ptmalloc2 to FreeBSD. The performance increase is 
> steller to put it mildly, even with FreeBSD's poor multithreading 
> performance. You're talking ten or more times faster in heavily 
> multithreaded code :)

<bad joke>

No, don't do that - with this in current and the new libthr, when
someone tries to benchmark mysql it will run so fast that time itself
will start running backwards!

</bad joke>