Merge branch 'jk/delta-chain-limit' into maint

"git repack --depth=<n>" for a long time busted the specified depth
when reusing delta from existing packs.  This has been corrected.

* jk/delta-chain-limit:
pack-objects: convert recursion to iteration in break_delta_chain()
pack-objects: enforce --depth limit in reused deltas

diff --cc builtin/pack-objects.c
Simple merge