clean installation of 643.

[Yoshiki Ohshima]

I tried to do clean install of 643 and it failed.  Actually, it worked
for the first time.  Then, I realized that I forgot to put Q2D05
firmware on my USB memory.  So I put the .rom file and tried the clean
installation again.  Then during the boot process I got:

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**** Restoring from backup ****
tar: Short read
Traceback (most recent call last):
  File "/init", line 110, in <module>
    backup_or_restore()
  File "/init", line 87, in backup_or_restore
    do_restore()
  File "/init", line 77, in do_restore
    safe_sh("tar -xz -f " + backup_file + " -C /restore")
  File "/initutil.py", line 26, in safe_sh
    raise RuntimeError("Command exited with non-zero exit status.")
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-- Yoshiki