Avoid integer overflow in assertion.
Avoid integer overflow in assertion.

Ignore-this: ad5c515fb6407d1a4ea5e68ed2d123ea
From Fabian Keil.

darcs-hash:20090315043458-4cc09-c787d036dfc94ae342bafa6d0861b819b19491b4.gz

toke/polipo,Psiphon-Inc/polipo,ssb22/polipo2,ssb22/polipo2,feijilei/polipo,ajmgh/polipo,nxtreaming/chumen,doublec/namecoin-polipo,caeies/polipo-caeies,strongwillow/polipo,lkraider/polipo,feijilei/polipo,galeksandrp/polipo,Android-Apps/polipo,feijilei/polipo,akkakks/polipo,strongwillow/polipo,Android-Apps/polipo,fukusaka/polipo,lkraider/polipo,fqtools/polipo,fqtools/polipo,lkraider/polipo,nxtreaming/chumen,jeromelebel/polipo,dxq-git/polipo,dxq-git/polipo,danchr/polipo,jech/polipo,berkley4/polipo,jech/polipo,akkakks/polipo,ssb22/polipo2,TierraDelFuego/opilop,galeksandrp/polipo,galeksandrp/polipo,akkakks/polipo,nxtreaming/chumen,berkley4/polipo,fqtools/polipo,jech/polipo,gorakhargosh/polipo,dxq-git/polipo,berkley4/polipo,clowwindy/polipo