grep: display correct user/revision for --all in reverse. Also handle multiple occurrences of the same line by storing linestates in an array instead of a dict, and using difflib to compute the difference between linestates.

#!/bin/sh

hg init

echo "Is there an error message when trying to diff non-existing files?"
hg diff not found

echo "Is there an error message when trying to add non-existing files?"
hg add not found