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Convert a TOPS-20 file transferred in FTP "binary" mode to "tenex" mode.
In "binary" mode, we have 2 36-bit words in 9 8-bit bytes. In "tenex"
mode, we want the top 32 bits of each 36-bit group, giving 8 8-bit bytes.
Who knows what FTP did if the file had an odd number of 36-bit words.