crypto/tls: Add SSL 3.0 support

[gopherbot]

by kai@tinkercad.com:

tinkercad.com was seeing 10%-15% of our users fail to connect to our https servers due
to the browser using SSL 3.0 instead of TLS 1.0. agl speculates that this might occur
both due to misconfigurations and due to browser automatically downgrading from TLS 1.0
to SSL 3.0.

For sites running https a recommendation would be to monitor any http/https transitions
to try to verify how much of their population is running into this issue.

As per offline discussion, please file this bug against agl to track adding SSL 3.0
support to crypto/tls.

[robpike]

Comment 1:

Labels changed: added packagechange, security.

Owner changed to @agl.

Status changed to Accepted.

[agl]

Comment 2:

This issue was closed by revision a775fbf.

Status changed to Fixed.