py: Include mpconfig.h before all other includes.

It defines types used by all other headers.

Fixes #691.
diff --git a/py/malloc.c b/py/malloc.c
index b180ddf..8e90849 100644
--- a/py/malloc.c
+++ b/py/malloc.c
@@ -28,8 +28,8 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "misc.h"
 #include "mpconfig.h"
+#include "misc.h"
 
 #if 0 // print debugging info
 #define DEBUG_printf DEBUG_printf