Enforce namespace unique constraints

This is the update to actually enable namespace support.

At the moment, I pass a namespace as a query parameter in order to support namespace scoping on the v1beta urls.  Once v1beta3 lands, I will modify to pass namespace in the path.  Note the client libraries were modified to make this easy to do, so should be a trivial change once ready.

I broke the commits into logical sections to improve readability.
Final answer: is this PR done enough to commit tomorrow?

@lavalamp @derekwaynecarr @smarterclayton

On Wed, Oct 15, 2014 at 10:54 AM, Daniel Smith <notifications@github.com>
wrote:

> In pkg/api/context.go:
>
> > @@ -71,3 +77,12 @@ func ValidNamespace(ctx Context, resource *TypeMeta) bool {
> >  	}
> >  	return ns == resource.Namespace && ok
> >  }
> > +
> > +// WithNamespaceDefaultIfNone returns a context whose namespace is the default if and only if the parent context has no namespace value
>
> Fine with me, we can merge and fix up later.
>
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