crypto/ssh: Handle msgUserAuthBanner during keyboard-interactive auth.
crypto/ssh: Handle msgUserAuthBanner during keyboard-interactive auth.

R=agl, golang-dev
CC=golang-dev
https://codereview.appspot.com/12983046

Committer: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

xman1101/terminal,tonnerre/golang-go.crypto,polydawn-ports/go.crypto,drhax9908/go.crypto,polydawn-ports/go.crypto,tonnerre/golang-go.crypto,drhax9908/go.crypto,isislovecruft/go.crypto,xman1101/terminal,dizzyd/go.crypto,isislovecruft/go.crypto,dizzyd/go.crypto