D2 phobos BigInt bug

[dsimcha]

== Quote from ZHOU Zhenyu (rinick at goozo.net)'s article
> BigInt b = "100000";
> foreach( i; 1..20 ){
>     b*=10;
>     writeln(b*b);
> }
> system: Windows
> CPU: Intel Core2 Duo T7250 2.00GHz
> result:
> 1000000000000
> 100000000000000
> 10000000000000000
> 1000000000000000000
> 100000000000000000000
> 10000000000000000000000
> 999981553255926290448384
> 100000000000000000000000000
> 10000000000000000000000000000
> 1000000000000000000000000000000
> 100000000000000000000000000000000
> 10000000000000000000000000000000000
> 1000000000000000000000000000000000000
> 100000000000000000000000000000000000000
> 10000000000000000000000000000000000000000
> 999999999999999999999981553255926290448384
> 100000000000000000000000000000000000000000000
> 9999999999999999999999999981553255926290448384
> 1000000000000000000000000000000000000000000000000

Yep, I can reproduce that on Windows on an Athlon 64 X2.  You're _not_ just going
crazy.  Please file a Bugzila.