Backout ad09ce1d393c and replace ''' with """ to make some highlighting happy. I have tried Debian's default emacs and the current CVS version. Default emacs doesn't have highlighting enabled (and being emacs-illiterate I don't know how to enable it) and the CVS emacs' Python highlighting has no problems with ' characters here.

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"

echo 123 > b
hg add b
hg diff --nodates

hg diff --nodates -r tip

echo foo > a
hg diff --nodates

hg diff -r ""
hg diff -r tip -r ""

true