Fix new tests to be better. In particular, fix webraw test to
specify a date on commit to be less brittle, and fix test-oldcgi to test
fetching a subdirectory of a webdir instance.
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory