Merge remote-tracking branch 'origin/master' into repobrowse

* origin/master:
  config: do not slurp lines into memory
  TODO: several updates
  search: schema version bump for empty References/In-Reply-To
  Revert "searchidx: reindex clobbers old thread IDs"
  searchidx: reindex clobbers old thread IDs
  searchidx: deal with empty In-Reply-To and References headers
  searchview: increase limit for displaying search results
  searchview: clarify numeric summary at bottom
  add filter for Subject: tags
  watchmaildir: allow arguments for filters
  watchmaildir: limit live importer processes
  learn: implement "rm" only functionality
  mime: avoid SUPER usage in Email::MIME subclass
  inbox: reinstate periodic cleanup of Xapian and SQLite objects
  introduce PublicInbox::MIME wrapper class

diff --cc MANIFEST
Simple merge

diff --cc lib/PublicInbox/Inbox.pm
Simple merge

diff --cc lib/PublicInbox/SearchIdx.pm
Simple merge