tests/test-merge5.out

dirstate: fix rebuild; add a test

If rebuild calls invalidate, it will just queue a (re)read of the dirstate
file, while what we really want is to empty the current state.

1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
abort: update spans branches, use 'hg merge' or 'hg update -C' to lose changes