Merge branch 'np/maint-safer-pack'

* np/maint-safer-pack: fixup_pack_header_footer(): use nicely aligned buffer sizes index-pack: use fixup_pack_header_footer()'s validation mode pack-objects: use fixup_pack_header_footer()'s validation mode improve reliability of fixup_pack_header_footer() pack-objects: improve returned information from write_one()