[MERGE] Checkout into existing trees works

[John Arbash Meinel]

John Arbash Meinel has voted approve.
Status is now: Approved
Comment:
I think it was actually a case of us actually wanting to prevent it. 
Because we felt that checking out into an existing directory was a bad 
idea. (And usually meant someone had a typo, like doing:
cd base
bzr checkout subdir
)

Have you checked what sort of error that will produce?

So I think we've reversed our decision on not letting people do that 
(and TT.build_tree should correctly handle when there are already files 
in the target directory anyway, so that portion should be handled)

So I'm okay with your changes. You should probably wait until tomorrow 
to merge in case someone else has a different viewpoint.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C46C338FB.9060202%40utoronto.ca%3E