I think the ideal behavior (back-compat aside) is that if a user explicitly sets a profile name and we can't find it anywhere (shared creds, boto config, etc) then we should raise an exception letting them now.  I think it's potentially dangerous to fall back to other creds.    If I set my profile name to `dev` and the actual profile name is `development`, we fall back to `default` or even `Credentials` in the boto config which might be problematic if those were the root credentials.  It seems reasonable to qualify this as a bug fix.