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).
#!/bin/sh
hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"
echo 123 > b
hg add b
hg diff --nodates
hg diff --nodates -r tip
echo foo > a
hg diff --nodates
hg diff -r ""
hg diff -r tip -r ""
true