Well, this turned out a lot of problems. Currently blocked by ITS#6138 Bad Cancel/Abandon/"internal abandon"/Syncprov interactions.

back-relay/op.c done (ITS#6133). syncprov/retcode issues may fit better under ITS#6138.

Bitflags should be unnecessary as such, just need a set of values. Though it wouldn't hurt if they were chosen so one could use bit operations to reduce checks for "o_abandon == A or B". "Suppress response" value mentioned in ITS#6138 also needed, maybe that must be a bitflag when combined with Cancel stuff.

Some tidbits uglifying a fix: * op->o_conn->c_mutex is locked when be->be_abandon() is called, but not when be->be_cancel() is called. * send_ldap_ber() needs the lock while it holds &conn->c_write1_mutex, but code elsewhere indicates the reverse lock order.

Question: syncprov_op_abandon() holds &si->si_ops_mutex when setting so->s_op->o_abandon. Does it need that? The function needs to grab op->o_conn->c_mutex when called as Cancel, but must not do that while holding &si->si_ops_mutex since Abandon grabs the locks in the opposite order.