py: Move to guarded includes, everywhere in py/ core.

Addresses issue #1022.

py/objtype.h

@@ -23,6 +23,10 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+#ifndef __MICROPY_INCLUDED_PY_OBJTYPE_H__
+#define __MICROPY_INCLUDED_PY_OBJTYPE_H__
+
+#include "py/obj.h"
 
 // instance object
 // creating an instance of a class makes one of these objects
@@ -36,3 +40,5 @@ typedef struct _mp_obj_instance_t {
 // these need to be exposed so mp_obj_is_callable can work correctly
 bool mp_obj_instance_is_callable(mp_obj_t self_in);
 mp_obj_t mp_obj_instance_call(mp_obj_t self_in, mp_uint_t n_args, mp_uint_t n_kw, const mp_obj_t *args);
+
+#endif // __MICROPY_INCLUDED_PY_OBJTYPE_H__