Rename tls13_prepare_* to tls13_add_*.

The SSL code suffers from needing too many verbs for variations on
writing things without actually writing them. We used to have queuing
the message up to be written to the buffer BIO, writing to the buffer
BIO, and flushing the buffer BIO. (Reading, conversely, has a similar
mess of verbs.)

Now we just have adding to the pending flight and flushing the pending
flight, match the SSL_PROTOCOL_METHOD naming.

BUG=72

Change-Id: I332966928bf13f03dfb8eddd519c2fefdd7f24d4
Reviewed-on: https://boringssl-review.googlesource.com/13227
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/tls13_server.c b/ssl/tls13_server.c
index c7096fc..09b9cfe 100644
--- a/ssl/tls13_server.c
+++ b/ssl/tls13_server.c
@@ -471,7 +471,7 @@
       goto err;
     }
 
-    if (!tls13_prepare_certificate(hs)) {
+    if (!tls13_add_certificate(hs)) {
       goto err;
     }
 
@@ -489,7 +489,7 @@
 
 static enum ssl_hs_wait_t do_send_server_certificate_verify(SSL_HANDSHAKE *hs,
                                                             int is_first_run) {
-  switch (tls13_prepare_certificate_verify(hs, is_first_run)) {
+  switch (tls13_add_certificate_verify(hs, is_first_run)) {
     case ssl_private_key_success:
       hs->tls13_state = state_send_server_finished;
       return ssl_hs_ok;
@@ -508,7 +508,7 @@
 
 static enum ssl_hs_wait_t do_send_server_finished(SSL_HANDSHAKE *hs) {
   SSL *const ssl = hs->ssl;
-  if (!tls13_prepare_finished(hs) ||
+  if (!tls13_add_finished(hs) ||
       /* Update the secret to the master secret and derive traffic keys. */
       !tls13_advance_key_schedule(hs, kZeroes, hs->hash_len) ||
       !tls13_derive_application_secrets(hs) ||