debugrebuildstate: clarify that rev can't be specified without -r
-r has a default value of '' in the command line. The function default value of
'tip' is thus never used and any attempt at specifying revisions without -r
will fail.
It seems like then intended behavior was that 'hg debugrebuildstate' without
any parameters should set the parents to tip. That would be very confusing now
when the command primarily is used to recover from incorrect stat info.
It is apparently undocumented that '' is the same as '.' ... unless it is
passed in a place where revsets are used.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..