I forgot about this feature when I was implementing
blob-ID-based searches :x
* make "git cat-file --batch" detect unlinked packfiles so we don't
have to restart processes (very long-term)
* make "git cat-file --batch" detect unlinked packfiles so we don't
have to restart processes (very long-term)
+
+* support searching based on `git-patch-id --stable` to improve
+ bidirectional mapping of commits <=> emails