> I tried SL2 and it quite happily ignored the fact that the file had changed.
Weird. I use Sublime Text 2 exclusively across all three platforms. Whenever an open file changes (e.g. I sync to Perforce), it pops up a modal dialog box when I bring that file's tab back into focus. If you're referring to a file that's changed in the background as you're actively editing it, I admit I haven't tried that.