Fix relay_command_to_string(); solve 12700.

Two bugs here:
  1) We didn't add EXTEND2/EXTENDED2 to relay_command_to_string().

  2) relay_command_to_string() didn't log the value of unrecognized
     commands.

Both fixed here.
Merge remote-tracking branch 'public/bug12700_024' into maint-0.2.5