Include-what-you-use ssl/internal.h.

The rest of ssl/ still includes things everywhere, but this at least fixes the
includes that were implicit from ssl/internal.h.

Change-Id: I7ed22590aca0fe78af84fd99a3e557f4b05f6782
Reviewed-on: https://boringssl-review.googlesource.com/4281
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 81e76c4..eae6ff3 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -150,17 +150,18 @@
 
 #include <assert.h>
 #include <stdio.h>
+#include <string.h>
 
 #include <openssl/buf.h>
 #include <openssl/bytestring.h>
 #include <openssl/rand.h>
 #include <openssl/obj.h>
+#include <openssl/err.h>
 #include <openssl/evp.h>
 #include <openssl/mem.h>
 #include <openssl/md5.h>
 #include <openssl/dh.h>
 #include <openssl/bn.h>
-#include <openssl/engine.h>
 #include <openssl/x509.h>
 
 #include "internal.h"