hg status will now show "R filename" for "hg rm"ed files and
"! filename" for files which were deleted manually.
Manually deleted files are considered unmodified.
it works almost the same as git-bisect:
hg bisect init # start bisecting
hg bisect bad # mark current revision as broken
hg bisect good [<rev>] # mark <rev> as working
... the bisect code finds a new revision to try
... see if it works
hg bisect good # if it worked
hg bisect bad # it doesn't work
continue until there is only one revision left
