How things are now:
top of tree is in ~/project/
cd ~/project/foo
vim file
# make changes and save/quit
arc diff file
# Usage Exception: There are no changes to generate a diff from!
cd ..
arc diff foo/file
# diff is created
How things should be:
top of tree is in ~/project/
cd ~/project/foo
vim file
# make changes and save/quit
arc diff file
# diff is created