demandimport: patch __builtin__ instead of __builtins__
This helps on implementations other than CPython, where __builtins__ isn't
necessarily defined (as it's an implementation detail for CPython).
dirty
M foo
% validate update of standalone execute bit change
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
nothing changed
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
0 files updated, 0 files merged, 0 files removed, 0 files unresolved