fix traceback of extdiff after a merge
- files that comes from a different branch are marked as modified
but aren't present in the original manifest
- add a testcase for extdiff and for regular diff
#!/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