[MERGE] remove has_key() usage

[Martin Pool]

On 31 Aug 2006, John Arbash Meinel <john at arbash-meinel.com> wrote:
> Actually, we already have a 'bzrlib/tests/test_api.py' file, which was
> used to ensure that we weren't creating WorkingTree objects inside
> Branch (WT should know about a B but not really the other way).
> 

We also have test_source, and it might be good to write a check there
for no more calls to has_key().  

I try not to have trailing whitespace on new commits but I don't
strongly either way about fixing existing code.

-- 
Martin