Add code to bdb_attribute and bdb_group where use TXN id and to
provide error, but need to rework callers (and their callers) to
ensure error is properly bubbled up to the backend operation routine
handling the transaction.  Ugh.

rework them slightly to avoid computations which might result in underflow.
Rename them for consistency with other berval routines.
Remove some utf8 lint.

added ber_[mem|case]cmp() macros for fast berval comparison; extensively used in acl and in dn_match macro at present

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

U-Mich allows someone with selfwrite to use replace all values
of an attribute with a value containing their DN.  Which, of course,
could than be deleted.  This behavior was carried forward in all
versions of OpenLDAP.

The new semantics separate checks for deleting all existing values
and adding new values.  It is more logical and more inline with
the common use of selfwrite.

of UTF8 string. (Returns charlen if valid, 0 if not.)