Implement our ExtendBzrTestSuite as per the spec.

[John Arbash Meinel]

Robert Collins wrote:
> Well, not -quite- as per the spec, our test environment has mutated
> since the spec was written. But pretty close anyhow.
> 
> -Rob
> 

You forgot to describe whether this is "RFC" or "MERGE".

And to summarize, this allows us to have tests fail for "platform
deficiencies" (like no symlink support), or for "known failures" (things
that we may not support on all platforms, or test cases that we want to
pass in the future, but don't have working yet).

My only concern for the missing feature support (_test_needs_features),
is that it is set at the class level.  All it really means is that we
have to split our current test classes into regular ones, and ones that
require specific features.

It is a little bit easier in the tests to just raise NeedsSymlinks, or
something like that. (I see it as a bigger issue when we have multiple
things, like maybe a test NeedsParamiko and NeedsSymlinks, or something,
but we can just use another TestCase for that).

I do really like how you report what features were missing, and how many
tests were skipped as a result.

So overall, +1. I just had a minor comment about doing it in a different
way.

John
=:->