Deprecate quite a few recursive includes from the ssl.h API header and
remove some unnecessary includes from the internal header ssl_locl.h. This
then requires adding includes for bn.h in four C files.

ssl/ssl.h

diff --git a/ssl/ssl.h b/ssl/ssl.h
index 8a16d77..04909c8 100644
--- a/ssl/ssl.h
+++ b/ssl/ssl.h
@@ -178,9 +178,16 @@
 #ifndef OPENSSL_NO_BIO
 #include <openssl/bio.h>
 #endif
+#ifndef OPENSSL_NO_DEPRECATED
 #ifndef OPENSSL_NO_X509
 #include <openssl/x509.h>
 #endif
+#include <openssl/crypto.h>
+#include <openssl/lhash.h>
+#include <openssl/buffer.h>
+#endif
+#include <openssl/pem.h>
+
 #include <openssl/kssl.h>
 #include <openssl/safestack.h>
 #include <openssl/symhacks.h>
@@ -318,11 +325,6 @@
 }
 #endif
 
-#include <openssl/crypto.h>
-#include <openssl/lhash.h>
-#include <openssl/buffer.h>
-#include <openssl/pem.h>
-
 #ifdef  __cplusplus
 extern "C" {
 #endif