Revert almost all of 5be434785317; add a test
Because of file copies, we should update the manifest dict only after
committing all files.
#!/bin/sh
hg init dir
cd dir
echo bleh > bar
hg add bar
hg ci -m 'add bar'
hg cp bar foo
echo >> bar
hg ci -m 'cp bar foo; change bar'
hg debugrename foo
hg debugindex .hg/data/bar.i