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_client.c b/ssl/tls13_client.c
index 518c4dc..774b806 100644
--- a/ssl/tls13_client.c
+++ b/ssl/tls13_client.c
@@ -482,7 +482,7 @@
   }
 
   if (!ssl_auto_chain_if_needed(ssl) ||
-      !tls13_prepare_certificate(hs)) {
+      !tls13_add_certificate(hs)) {
     return ssl_hs_error;
   }
 
@@ -499,7 +499,7 @@
     return ssl_hs_ok;
   }
 
-  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_complete_second_flight;
       return ssl_hs_ok;
@@ -540,7 +540,7 @@
   }
 
   /* Send a Finished message. */
-  if (!tls13_prepare_finished(hs)) {
+  if (!tls13_add_finished(hs)) {
     return ssl_hs_error;
   }