Since updating to Mavericks, my screen captures of entire windows (using shift-cmd-4 and then the spacebar to toggle to window-capture mode) are saved with a white background frame added, so the window captured casts an arty shadow on it.

I know there's a terminal command to switch this off (because I've used it before), but I can't remember what it is, and I can't find it. Anyone know the one I mean?
If it's brokenless, don't suffix it...