On Restore from backup make LinkedFilesDir correct

* LT-13354
Message suggesting change of Linked Files folder not shown
in release build.

* Also this issue was fixed where version 6 backup was not restoring
  properly. It seems that there is some inconsistancy in the way
  filenames are stored in the backup files.
* LT-13054 Old default location Media files not restored from a FW7
  backup that includes them.

* The above was Ricks's work. I added a couple of tests.

Change-Id: I19c6f988434e72e6ab05bed22a9a4d29439c848c