ldb: added version 1.5.4

ldb is a LDAP-like embedded database. It is not at all LDAP standards
compliant, so if you want a standards compliant database then please see the
excellent OpenLDAP project.

What ldb does is provide a fast database with an LDAP-like API designed to be
used within an application. In some ways it can be seen as a intermediate
solution between key-value pair databases and a real LDAP database.

ldb is the database engine used in Samba4.

Features:
* The main features that separate ldb from other solutions are:
* Safe multi-reader, multi-writer, using byte range locking
* LDAP-like API
* fast operation
* choice of local tdb or remote LDAP backends
* integration with talloc
* schema-less operation, for trivial setup
* modules for extensions (such as schema support)
* easy setup of indexes and attribute properties
* LDIF for import/export
* ldbedit tool for database (via LDIF) editing (reminiscent of 'vipw')

(adam)