Avoid using s-expr, pkcs1-conv, and lsh-export-key.
Avoid using s-expr, pkcs1-conv, and lsh-export-key.

Instead we now use M2Crypto and struct.pack to construct it on our own.

This removes a dependency on nettle-bin and lsh-utils (which were never
specified in debian/control).

joshuamckenty/yolo-octo-wookie,sorenh/cc,joshuamckenty/yolo-octo-wookie,sorenh/cc,sorenh/cc