Merge branch 'tb/fix-midx-rename-while-mapped'

The codepath to write a new version of .midx multi-pack index files has learned to release the mmaped memory holding the current version of .midx before removing them from the disk, as some platforms do not allow removal of a file that still has mapping. * tb/fix-midx-rename-while-mapped: midx.c: guard against commit_lock_file() failures midx.c: lookup MIDX by object directory during repack midx.c: lookup MIDX by object directory during expire midx.c: extract MIDX lookup by object_dir