[PATCH 0/4] Add git-pack-intersect

This patch series adds git-pack-intersect. It finds redundant packs
by calculating the union of all objects present in .git/objects/pack
and then computing the smallest set of packs which contain all the
objects in this union.

It is quite fast, if I may say so myself. On my AMD3200+ it manages
to minimize a linux-2.6 repository with 9 pack files totaling 430MB
in ~0.7 seconds. The remaining packfiles total 102MB, which is a nice
reduction.

git-fsck-objects reports no errors after pruning, but the algorithm is 
not proven correct so backups might be in order before this gets more
testing.

/Lukas