Add test for renego client_version quirk.

In upstream's f4e1169341ad1217e670387db5b0c12d680f95f4, the client_version was
made constant across renegotiations, even if the server negotiated a lower
version. NSS has the same quirk, reportedly for SChannel:

https://code.google.com/p/chromium/codesearch#chromium/src/net/third_party/nss/ssl/ssl3con.c&sq=package:chromium&l=5103

Add a test to ensure we do not regress this.

Change-Id: I214e062463c203b86a9bab00f8503442e1bf74fe
Reviewed-on: https://boringssl-review.googlesource.com/2405
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/runner/common.go b/ssl/test/runner/common.go
index 02ee7e2..628c208 100644
--- a/ssl/test/runner/common.go
+++ b/ssl/test/runner/common.go
@@ -577,6 +577,11 @@
 	// CertificateRequest message. None the less, the configured set will
 	// still be enforced.
 	NoSignatureAndHashes bool
+
+	// RequireSameRenegoClientVersion, if true, causes the server
+	// to require that all ClientHellos match in offered version
+	// across a renego.
+	RequireSameRenegoClientVersion bool
 }
 
 func (c *Config) serverInit() {