objtype: Separate __new__ and __init__ methods.

Now schedule is: for native types, we call ->make_new() C-level method, which
should perform actions of __new__ and __init__ (note that this is not
compliant, but is efficient), but for user types, __new__ and __init__ are
called as expected.

Also, make sure we convert scalar attribute value to a bound-pair tight in
mp_obj_class_lookup() method, which avoids converting it again and again in
its callers.

py/qstrdefs.h

@@ -34,6 +34,7 @@ Q(__class__)
 Q(__doc__)
 Q(__import__)
 Q(__init__)
+Q(__new__)
 Q(__locals__)
 Q(__main__)
 Q(__module__)