Create Warning/Error when include directory does not exist

[gmoro]

I had a typo in one of the include (capital vs non-capital letters) and I just didn't get the include in place with no warning, if path not found we should do something about it.

[jgleissner]

That keg doesn't throw an error is intentional, as it is fine to reference sub directories that may not exist. If you for example have additional settings (like, billing codes) in a private repository you can still include those in a public recipe, and when generating from the public recipe only you'd simply miss those.

A warning however may certainly be in order. I'm just a little concerned that people could start worrying about warnings when building from a repo setup such as described, even though it's perfectly fine. We could make it a debug message, but that makes mistakes harder to miss, of course.

[rjschwei]

Yes, we need the capability to have overlays of multiple recipe trees and things being in different locations. As such triggering an error is not an option. I would also not make it a warning as we do not want to train people to ignore warnings. That said, I could see that an info message would be helpful, such as "skipping: 'foo' not found"

[jgleissner]

An info would be a good middle ground. People might still wonder whether there's something wrong though when they see the message, but it's probably better than hiding the message in the debug output.