always use DB_AUTO_COMMIT when opening a database, don't make it
  dependent on an in-progress transaction

  use mutex instead of DB lock for db access.

the commandline

The oblique SLAPI interface requires that preop bind plugins return 1 in the
case that they have authoritatively handled the bind; of course, this is
the same return value that doPluginFNs() returns in the case of no plugins
being called.

This patch should distinguish between the two cases...

  note that -lltdl is added redundantly if --enable-modules was specified.
It seems to me that --enable-slapi should have implied --enable-modules
from the beginning.

- if test back-ldbm then
-    run the provider with back-bdb when back-bdb is configured
-    run the provider with back-hdb when back-hdb is configured
-    exit when neither is configured

Note that the mech stored in the void *defaults structure is useless
because we can't look inside the structure, and the mech list is needed
as input to the SASL library, before any callbacks are called. It seems
the mech doesn't belong in the *defaults struct, and/or it should be
visible and not opaque.

on arbitrary EntryInfo.

usage - necessary to use larger types for interop with a certain client
that would expect the assertion (attr:1.2.840.113556.1.4.803:=2147483648)
to match a signed value (eg. -2147483646).

There are probably better / more portable solutions; review appreciated.

  moved labeledURI into system schema
  attribute types that inherit from labeledURI may be used in dynamic
    groups e.g. access to * by group/groupOfURLs/memberURL=foo