crypto/tls: Support ECDSA keys in generate_cert.go
crypto/tls: Support ECDSA keys in generate_cert.go

R=golang-codereviews, bradfitz, agl
CC=golang-codereviews
https://codereview.appspot.com/117180043

Committer: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old