py: Change all uint to mp_uint_t in obj.h.

Part of code cleanup, working towards resolving issue #50.
diff --git a/py/objexcept.c b/py/objexcept.c
index 6064291..6cf9cbc 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -296,7 +296,7 @@
     return mp_obj_new_exception_args(exc_type, 1, &arg);
 }
 
-mp_obj_t mp_obj_new_exception_args(const mp_obj_type_t *exc_type, uint n_args, const mp_obj_t *args) {
+mp_obj_t mp_obj_new_exception_args(const mp_obj_type_t *exc_type, mp_uint_t n_args, const mp_obj_t *args) {
     assert(exc_type->make_new == mp_obj_exception_make_new);
     return exc_type->make_new((mp_obj_t)exc_type, n_args, 0, args);
 }