slapd: LDAPv3 simple bind

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

I've committed changes such that -devel slapd will
accept a LDAPv3 simple bind request.  I've also
added support to our test suite to optionally use
LDAPv3:
  env LDAP_PROTO=3 make ldbm

Of course, the LDAPv3 support is incomplete... this
change is purely to facilate development.

Kurt