dirstate.remove: during merges, remember the previous file state...
dirstate.remove: during merges, remember the previous file state
We encode the previous state as a negative file size (AFAICS, previous
versions of hg always have size == 0 when state == 'r').
We save the state of 'm'erged and dirty files, because they're the
two states that indicate that a file has to be committed on a merge
to correctly record per-file history.
