Emacs support: numerous changes. Most SCM commands now work in derived buffers (e.g. diff viewing buffers) as well as buffers backed by files. diff and log now work properly on repositories and files. Commit support is more solid. Doc strings are better.

#!/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