Re: (ITS#6157) unAbandonable operations aren't.

Suggested partual fix - add this possible value for o_cancel: #define SLAP_CANCEL_INVALID 0x04 /* like 0 but prevents Cancel */

Something like this: http://folk.uio.no/hbf/OpenLDAP/cancel-cancel.txt

Does not reject abandon(Cancel/StartTLS), would need to extend o_cancel with yet another value. That's ugly enough already, so I let that wait. connection_abandon() in particular isn't invalid client action, but it shouldn't be worse than causing a surprising result code or not response before closing the connection.

Does not address syncprov's Cancel handler.

I don't know if the bconfig.c pathces are correct, but need to reject cancel before (reacting to) thread pool pauses there and maybe in syncrepl/syncprov.