The client_version needs to be preserved, both for the RSA key exchange and
(when this codepath is used for TLS) for the SChannel renego workaround. Fix
the tests to enforce this so the cipher suite version tests catch this.

Change-Id: I0c42dc3ec4830f3724026b400e5066e7a7f1ee97
Reviewed-on: https://boringssl-review.googlesource.com/2551
Reviewed-by: Adam Langley <agl@google.com>

pskKeyAgreement is now a wrapper over a base key agreement.

Change-Id: Ic18862d3e98f7513476f878b8df5dcd8d36a0eac
Reviewed-on: https://boringssl-review.googlesource.com/2053
Reviewed-by: Adam Langley <agl@google.com>

Only the three plain PSK suites for now. ECDHE_PSK_WITH_AES_128_GCM_SHA256 will
be in a follow-up.

Change-Id: Iafc116a5b2798c61d90c139b461cf98897ae23b3
Reviewed-on: https://boringssl-review.googlesource.com/2051
Reviewed-by: Adam Langley <agl@google.com>

These were added in TLS 1.2. They are like the standard AES-CBC cipher suites,
but use different HMACs.

Change-Id: Ib89ddebd1aa398b1347f8285f5d827068b1bd181
Reviewed-on: https://boringssl-review.googlesource.com/1730
Reviewed-by: Adam Langley <agl@google.com>

Run against openssl s_client and openssl s_server. This seems to work for a
start, although it may need to become cleverer to stress more of BoringSSL's
implementation for test purposes.

In particular, it assumes a reliable, in-order channel. And it requires that
the peer send handshake fragments in order. Retransmit and whatnot are not
implemented. The peer under test will be expected to handle a lossy channel,
but all loss in the channel will be controlled. MAC errors, etc., are fatal.

Change-Id: I329233cfb0994938fd012667ddf7c6a791ac7164
Reviewed-on: https://boringssl-review.googlesource.com/1390
Reviewed-by: Adam Langley <agl@google.com>

Use it to test DHE-RSA in BoringSSL.

Change-Id: I88f7bfa76507a6f60234d61d494c9f94b7df4e0a
Reviewed-on: https://boringssl-review.googlesource.com/1377
Reviewed-by: Adam Langley <agl@google.com>

With this change, calling SSL_enable_fallback_scsv on a client SSL* will
cause the fallback SCSV to be sent.

This is intended to be set when the client is performing TLS fallback
after a failed connection. (This only happens if the application itself
implements this behaviour: OpenSSL does not do fallback automatically.)

The fallback SCSV indicates to the server that it should reject the
connection if the version indicated by the client is less than the
version supported by the server.

See http://tools.ietf.org/html/draft-bmoeller-tls-downgrade-scsv-02.

Change-Id: I478d6d5135016f1b7c4aaa6c306a1a64b1d215a6

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)