go.crypto/ssh: Add support for the pre-2006 RC4 cipher mode.
go.crypto/ssh: Add support for the pre-2006 RC4 cipher mode.

LGTM=hanwen
R=agl, hanwen
CC=golang-codereviews
https://codereview.appspot.com/86600044

Committer: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

polydawn-ports/go.crypto,isislovecruft/go.crypto,isislovecruft/go.crypto,polydawn-ports/go.crypto