Attribute replacement falling back to property and it shouldn't

[bob2517]

Getting the property id of the body node returns a type of "string" even when not explicitly set, which breaks inherited attribute replacement in the core because it thinks an id property is actually there. An id property must be being set internally in the browser.

I've split up the attr and prop return function as it was falling back to getting the property when it wasn't actually being asked for - which is unnecessary, and put in a better check for attribute existence, and the fix is now on the branch.

This fix will definitely need testing on a variety of production code before official release.

[bob2517]

Closing pending release.