x/crypto/ssh: suggested add auth methods from server to error info

[gopherbot]

by weyllor:

What does 'go version' print?
go version go1.2.1 windows/amd64

What steps reproduce the problem?
If possible, include a link to a program on play.golang.org.

1. config a Client only with password method
2. connect to a ssh server reject password method
3. auth fail, but no more info to find out what happened.

What happened?
not enough error info to known why ssh auth fail.

What should have happened instead?
show what methods supported by server in error info.

Please provide any additional information below.
I make a path for this issue, ref the attachment.

Attachments:

1. patch.diff (1379 bytes)

[ianlancetaylor]

Comment 1:

Labels changed: added repo-crypto.