when an object in the buffer gets replaced with another object for the same
tree position, delete the old object from .git/objects.)
+A git repo containing 10000 commits, starting with 10000 files and ending
+with 0, deleting 1 file per commit, weighs in at 99mb. That's with
+short filenames, more typical filenames would add to it. (It packs down to
+9 mb, but that's just extra work for objects that will get gc'ed away
+eventually.)
+
## slowness in writing git objects
git-annex uses git commit-tree to create new commits on the adjusted