pack negotiation algorithm between 2 share-nothing repos

This is a corner case that has a real use case:

git clone linux-2.6.git
cd linux-2.6
git remote add history git-history.git
git fetch history
# graft graft graft

Because history.gi and linux-2.6.git have nothing in common, the
server side keeps asking for more "have"s and the client keeps sending
in "git fetch history". Negotiation phase takes longer than my
patience so I abort it, hack git to send no "have"s and retry.

I know this is a corner case, but because it has a valid use case,
maybe we should do something about it. Immediate reaction is to add an
option to send no "have"s. But maybe you guys have better ideas.

PS. I know i'm behind my git inbox. Looking into it soon.
-- 
Duy