Auto-detect lack of microformat property-nested scoping and warn

E.G. if someone has a h-entry with p-comments _without_ a mf root classname, all of their properties will attach themselves to the parent h-entry and the p-comments will be strings.

Start by reproducing the h-entry and p-comments markup described in the issue, then locate the microformat property-scoping and warning entry points. Done means detecting a property-nested item without an mf root classname and warning instead of silently attaching its properties to the parent h-entry.

Written by the indexing model from the issue text.