[MERGE] Make selftest --parallel work

[Matt Nordhoff]

Vincent Ladeuil wrote:
> One-liner but not trivial.
> 
> I also made both sides of the pipe in fork_for_tests line
> buffered as I see no reason to have the writer be unbuffered
> while the reader is still line-buffered (they use a line-based
> protocol anyway).
> 
>           Vincent

> -                if type(result) == ThreadsafeForwardingResult:
> +                if type(test) == testtools.ConcurrentTestSuite:
> +                    # We need to catch bzr specific behaviors

Nit: You didn't introduce this, but you should use "isinstance(foo,
bar)" or "type(foo) is bar". Comparing types with == is weird.
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