Windows MSVC port

Extend the windows port so it compiles with the toolchain from Visual Studio 2013
diff --git a/py/objint.c b/py/objint.c
index c8bcb60..73b4c5d 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -303,7 +303,7 @@
 
     // convert the bytes to an integer
     machine_uint_t value = 0;
-    for (const byte* buf = bufinfo.buf + bufinfo.len - 1; buf >= (byte*)bufinfo.buf; buf--) {
+    for (const byte* buf = (const byte*)bufinfo.buf + bufinfo.len - 1; buf >= (byte*)bufinfo.buf; buf--) {
         value = (value << 8) | *buf;
     }