py: add variable argument exception constructor function.

Addresses issue #104.
diff --git a/py/obj.c b/py/obj.c
index 866be22..3e4164d 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -145,7 +145,7 @@
         return (machine_int_t)mp_obj_float_get(arg);
 #endif
     } else {
-        nlr_jump(mp_obj_new_exception_msg_1_arg(MP_QSTR_TypeError, "can't convert %s to int", mp_obj_get_type_str(arg)));
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "can't convert %s to int", mp_obj_get_type_str(arg)));
     }
 }
 
@@ -160,7 +160,7 @@
     } else if (MP_OBJ_IS_TYPE(arg, &float_type)) {
         return mp_obj_float_get(arg);
     } else {
-        nlr_jump(mp_obj_new_exception_msg_1_arg(MP_QSTR_TypeError, "can't convert %s to float", mp_obj_get_type_str(arg)));
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "can't convert %s to float", mp_obj_get_type_str(arg)));
     }
 }
 
@@ -180,7 +180,7 @@
     } else if (MP_OBJ_IS_TYPE(arg, &complex_type)) {
         mp_obj_complex_get(arg, real, imag);
     } else {
-        nlr_jump(mp_obj_new_exception_msg_1_arg(MP_QSTR_TypeError, "can't convert %s to complex", mp_obj_get_type_str(arg)));
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "can't convert %s to complex", mp_obj_get_type_str(arg)));
     }
 }
 #endif
@@ -204,11 +204,11 @@
             mp_obj_list_get(o_in, &seq_len, &seq_items);
         }
         if (seq_len != n) {
-            nlr_jump(mp_obj_new_exception_msg_2_args(MP_QSTR_IndexError, "requested length %d but object has length %d", (void*)n, (void*)(machine_uint_t)seq_len));
+            nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_IndexError, "requested length %d but object has length %d", n, seq_len));
         }
         return seq_items;
     } else {
-        nlr_jump(mp_obj_new_exception_msg_1_arg(MP_QSTR_TypeError, "object '%s' is not a tuple or list", mp_obj_get_type_str(o_in)));
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "object '%s' is not a tuple or list", mp_obj_get_type_str(o_in)));
     }
 }
 
@@ -220,10 +220,10 @@
             i += len;
         }
         if (i < 0 || i >= len) {
-            nlr_jump(mp_obj_new_exception_msg_1_arg(MP_QSTR_IndexError, "%s index out of range", type->name));
+            nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_IndexError, "%s index out of range", type->name));
         }
         return i;
     } else {
-        nlr_jump(mp_obj_new_exception_msg_2_args(MP_QSTR_TypeError, "%s indices must be integers, not %s", type->name, mp_obj_get_type_str(index)));
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "%s indices must be integers, not %s", type->name, mp_obj_get_type_str(index)));
     }
 }