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.
adding empty-file
adding large-file
adding another-file
removing empty-file
removing large-file
recording removal of large-file as rename to another-file (99% similar)
% comparing two empty files caused ZeroDivisionError in the past
2 files updated, 0 files merged, 1 files removed, 0 files unresolved
adding another-empty-file
removing empty-file
adding large-file
adding tiny-file
adding small-file
removing large-file
removing tiny-file
recording removal of tiny-file as rename to small-file (82% similar)
% should all fail
abort: similarity must be a number
abort: similarity must be between 0 and 100
abort: similarity must be between 0 and 100