Include OpenSSL's objects.h before bn.h.

Prevents compile errors on some platforms (at least old GCCs and AIX's
XLC compilers).

buffer.h

@@ -47,6 +47,7 @@ int	 buffer_get_ret(Buffer *, void *, u_int);
 int	 buffer_consume_ret(Buffer *, u_int);
 int	 buffer_consume_end_ret(Buffer *, u_int);
 
+#include <openssl/objects.h>
 #include <openssl/bn.h>
 void    buffer_put_bignum(Buffer *, const BIGNUM *);
 void    buffer_put_bignum2(Buffer *, const BIGNUM *);