tla-like changesets

[Stefan Ring]

> We think merge directives are a better solution than changesets, because
> they allow full merging, retaining history.  Merge directives are
> generated with the "send" command.

They are nice IF you actually WANT to retain history AND the 
repositories are related.

I have two use cases where each of the preconditions is not met, 
respectively.

1. Not retaining history -- when working in a repository with strict 
guidelines on the commit statements, I don't want to bother building 
such an elaborate text for every intermittent commit several times a 
day. So I just want to tweak and beat the thing into the final shape and 
only then commit to the official repo, with a single good and clean 
commit message. I also don't like cluttering the official repository 
with all those intermittent commits. I could do that with a changeset 
but not with a merge-directive.

2. Non-related repositories -- our current repository has been started 
during a time when we experimented heavily with bzr, and several large 
files were added and removed several times, causing the repository to 
become quite large. We wanted to do a clean cut and restart the 
repository from scratch by exporting the last revision and importing it 
into a new repo (there was nothing of interest in the old commit history 
anyway). Now I happen to have a branch forked back then that I would 
eventually like to merge into the new repository. I cannot do this with 
a merge directive because the two are not related. I could quite easily 
do this with a changeset, though.