Consistently use file status icons

I noticed that “read-only” file icons are displayed on the tabs when a file is opened but not when displayed in the Places (Explorer) sidebar. It would be nice if the read-only icon was used in both places.

It would also be nice if you were not allowed to make editing changes to a read-only file until you first changed the permissions. As it is, one could make changes to the file before noticing it was read-only. Perhaps an editor preferences setting? (I looked, but didn’t see one.)