Need to figure out what's up with ComputedKeyInfos.Copy()

[akalin]

It currently makes a shallow partial copy. The shallowness may be a bug, and the partial copy is almost certainly a bug.

Looking through the history and the surrounding code (it's used only in SigChain.LocalDelegate to make a copy of the last chain link's cki to modify), I'm guessing that it is indeed meant to be a deep copy.

The other part of this bug is figuring out the consequences of this bug and writing a regression test.