Forbid the server certificate from changing on renego.

This allows us to move the code from Chrome into BoringSSL itself.

BUG=126

Change-Id: I04b4f63008a6de0a58dd6c685c78e9edd06deda6
Reviewed-on: https://boringssl-review.googlesource.com/14028
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index dedabb0..2e0c808 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -4464,6 +4464,7 @@
 #define SSL_R_TOO_MUCH_SKIPPED_EARLY_DATA 270
 #define SSL_R_PSK_IDENTITY_BINDER_COUNT_MISMATCH 271
 #define SSL_R_CANNOT_PARSE_LEAF_CERT 272
+#define SSL_R_SERVER_CERT_CHANGED 273
 #define SSL_R_SSLV3_ALERT_CLOSE_NOTIFY 1000
 #define SSL_R_SSLV3_ALERT_UNEXPECTED_MESSAGE 1010
 #define SSL_R_SSLV3_ALERT_BAD_RECORD_MAC 1020