Change examples to use the new MD API and check ret code
diff --git a/programs/pkey/dh_client.c b/programs/pkey/dh_client.c
index 875d0b0..21c4a81 100644
--- a/programs/pkey/dh_client.c
+++ b/programs/pkey/dh_client.c
@@ -212,7 +212,11 @@
         goto exit;
     }
 
-    mbedtls_sha1( buf, (int)( p - 2 - buf ), hash );
+    if( ( ret = mbedtls_sha1_ext( buf, (int)( p - 2 - buf ), hash ) ) != 0 )
+    {
+        mbedtls_printf( " failed\n  ! mbedtls_sha1_ext returned %d\n\n", ret );
+        goto exit;
+    }
 
     if( ( ret = mbedtls_rsa_pkcs1_verify( &rsa, NULL, NULL, MBEDTLS_RSA_PUBLIC,
                                   MBEDTLS_MD_SHA256, 0, hash, p ) ) != 0 )