Tab icon for read-only files

Preventing the edition of read-only files will be annoying for people using source control, this would have to be bound to a setting if it's implemented.

I would expect any revision control plugins to automatically open the file for edit as soon as you start typing, which will make the file writable.  I've written a P4 plugin for SublimeText that does just this https://github.com/seanhoughton/SublimePerforce  At the very least, this could be an option to toggle.