Enable TLS 1.2 clients

SSLUtil fails to recognize TLS 1.2 packets. Regardless of whether
the server supports TLS 1.2, failure to recognize the header prevents
it from falling back to an earlier revision of the protocol.

The change enables forward compatibility. Based on my reading of the
TLS 1.2 RFC, I think the server should recognize versions higher than
it actually supports and reply with a lower version number. I assume
that as long as the TLS major version is unchanged, the header format
is compatible.
Signal end-of-stream when remote sends a CLOSE notification

GlobusGSSCredentialImpl fails when the remote initiates a proper
SSL shutdown. The patch changes the logic such that rather
than throwing a generic error, the new ClosedGSSException is
thrown. The InputStream implementation recognizes this exception
and signals end-of-stream to the caller.
Merge pull request #135 from gbehrmann/fix/ssl-close

Signal end-of-stream when remote sends a CLOSE notification
Merge pull request #133 from gbehrmann/fix/tls12

Enable TLS 1.2 clients