Clean up some error handling

Only dn_validate, dn_normalize, and dn_parent remain (for now).

liblber:ber_bvarray_{add,free}.

Use typedefs for all backend functions, to minimize work in future API
updates. (back-*/external.h will never need updating in the future.)

conn->c_dn,c_ndn, Access->a_dn_pat)

added backend-side support for on-the-fly operational attributes; added hasSubordinates to schema and back-ldbm

Plugged other small leaks.

to deal with glued subordinates.

together into a single searchable hierarchy.

   Changed AttributeDescription.{ad_cname,ad_lang} to struct berval everywhere
   Deleted ad_free() everywhere
   Added ad_mutex to init.c

The AttributeDescriptions are in a linked list hanging off of the
corresponding AttributeType.

add global, per backend and per op_ndn time/size soft, hard and to-be-checked limits (exploited by back-ldbm); see slapd.conf(5) for details

The old monitoring stuff has been removed; the new backend is
enabled by using --enable-monitor at configure time and requires

	database monitor

in slapd.conf to be activated.  At present it implements a subset
of the old monitoring options, and it should be extendable to
a number of different subsystems.  The search operation has been
implementd; it does not honor abandon or size/time limits, though.
The compare and the abandon operations are planned.

Copyright Pierangelo Masarati <ando@sys-net.it>; the code is provided
AS IS with NO GUARANTEE.  It can be used and distributed under the
conditions stated by the OpenLDAP Public License.

backendsyncfreq <seconds>.  Setting this automatically enables
dbnosync (because the synchronizer takes care of it).