Make warnings available beyond stdout

[azaroth42]

As the service returns a real manifest, there is no slot of non-fatal warnings.

Proposal: If debug is turned on, add a _warnings property to the top level resource and collect them all there.

[azaroth42]

@zimeon Thoughts on this approach?

[zimeon]

I like this approach -- would be even cooler if _warnings were added to any appropriate object (or at top if that doesn't make sense)