reverse cherry picking + merge docs

[David Muir]

In the docs for reverse cherry picking, it says to do:

bzr merge -r 10..9


which probably won't do as you expect, since it works off of the submit 
branch rather than the current branch. The docs are rather vague about 
this, and I had to dig around to figure out why it was grabbing the 
wrong revisions.

Since (from my experience) reverse cherry picking is usually done within 
the current branch, shouldn't merge run off of :this instead of :submit?

Also, it would be good if the docs mention that merge uses :submit as 
its default. Even in the docs for the submit_branch config setting, it 
only mentions that it's used by `bzr send`.

On another note, what should the submit branch be for the upstream 
branch? Should it be itself?

ie. I have:
trunk -> :submit = first feature branch I merged in
staging -> :submit = trunk
production -> :submit = staging

Cheers,
David