Use unsigned version format.
This way can use one additional bit, and when encountering invalid revlogs
with the first bit set don't produce python warnings or strange error messages.
#!/bin/sh
hg init a
cd a
hg init b
echo x > b/x
echo '# should print nothing'
hg st
echo '# should print ? b/x'
hg st b/x
hg add b/x
echo '# should print A b/x'
hg st
echo '# should forget b/x'
hg revert --all
echo '# should print nothing'
hg st b