Neither Inboxes nor ExtSearch objects were retrying correctly
when there are live git processes, but the inboxes were getting
rescanned for search or other reasons. Ensure the scan retries
eventually if there's live processes.
We also need to update the cleanup task to detect Xapian shard
count changes, since Xapian ->reopen is enough to detect any
other Xapian changes. Otherwise, we just issue an inexpensive
->reopen call and let Xapian check whether there's anything
worth reopening.
This also lets us eliminate the Devel::Peek dependency.