Resolves: bug 245815
    Bug Description: DS Admin Migration framework - cross platform support
    Reviewed by: nhosoi (Thanks!)
    Fix Description: There are basically three parts to cross platform support
    1) Allow a different physical server root than the logical server root.  This allows you to copy the old server root directory to the target machine, either by making a tarball or by a network mount.  Then you can migrate from e.g. /mnt/opt/fedora-ds, and specify that the real old server root was /opt/fedora-ds.  This is the distinction between the --oldsroot and --actualsroot parameters.
    2) Cross platform database migration requires the old data is converted to LDIF first.  Migration makes the simplifying assumption that the database LDIF file is in the old db directory and has the name of <old backend name>.ldif e.g. userRoot.ldif
    3) Cross platform replication migration doesn't preserve the state, so the changelog nor other associated state information can be migrated.
    I rewrote the old migration script to use the FileConn - this theoretically will allow us to support migration using an LDAP::Conn as well.
    I had to make some fixes to FileConn, primarily to support the root DSE.
    Platforms tested: RHEL4
    Flag Day: no
    Doc impact: Yes, along with the rest of the new migration framework.