how to browse shred repository for 'heads'?

[Alexander Belchenko]

I want to ask this question many times but actually don't ask before.
Today I do very bad mistake and break my work.

If I have shared repository how I can browse all revisions inside it, 
revsions that does not have childs? IIRC, Mercurial have command 'hg 
heads' that prints all such revisions in similar situation. Is bzr does 
not have this interface?

Use case for this command will be: user has shared repo with branches 
inside. If user eventually delete branch it lose information how to 
ressurect this branch (if this branch was not merged to another branch).

I think that browsing of revisions.knit should do what I want, but at 
this moment I don't understand how to do this.

--
Alexander