More for #7589
ITS#7740 back-meta: avoid blocking other threads

Don't lock other threads while trying to connect to remote node.
Merge remote-tracking branch 'origin/mdb.master'
ITS#7739 fix for empty nested include
Another BDB to MDB bit
ITS#7735 fix memctx usage in prev commit
Fix CONFIG_DELETE crash

Closing a connection can abandon its ops without going thru the threadpool,
so make sure to lock the si_ops_mutex before walking the list.
ITS#7700
Update sections 6.2.2.1, 6.2.3.3
ITS#7741 Fix entryDN index lookup

DN notfound is authoritative, don't ignore the result