You say CERT_CELL, I say CERTS_CELL, tomato, tomatoe
The spec spoke of CERT cells in some places and CERTS cells in others. I figured CERTS cells fit best with VERSIONS cells, so went with that in the spec.
Now the code needs to change too. Should be no troubles to switch since the rest of the world doesn't care what one Tor's code calls cell 129.
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