Code review comment for lp:~spiv/bzr/annotate-objectnotlocked-496590

This is a minimal fix for bug 496590 targetted to 2.0.x. <https://code.edge.launchpad.net/~spiv/bzr/command-cleanup/+merge/16943> has a much more comprehensive fix for pretty much all bugs of this sort in builtins.py, but it's obviously a bit too large to be sensible for 2.0.x.