Trac Ticket #169 - allow 389 to use db5
    
    https://fedorahosted.org/389/ticket/169
    
    Fix description:
    1. DB suffix ".db4" is changed to ".db" if the server is linked
       with db5 (libdb); it remains ".db4" if linked with db4.
    2. Fixed DB_VERSION macro to pick up the correct APIs for db5.
    3. DB upgrade flag DBVERSION_UPGRADE_4_5 is introduced and set
       once it is found the db4 to db5 upgrade is necessary.
       Upgrade from db4 to 5 requires cleaning up the region files
       (__db.##) then update transaction log files.  The database
       files are compatible.
    4. Added a code to db.m4 to check /usr/include/libdb/db.h.
       If /usr/include/db4/db.h does not exists AND libdb does,
       the db5 (libdb) header file is used.
       Note: package db4-devel and libdb-devel cannot coexist.