All tests with Command::cargo_bin() fail when just running "cargo test"

[assarbad]

If you haven't built fastmod using cargo build, seven out of the thirteen tests fail. Those are all the tests that invoke Command::cargo_bin().

I'll look into this more closely and hope there is a way to express that the binary needs to be built prior to running cargo test within the Cargo.toml, because even if the idea is that fastmod be run, it probably implies that the latest version ought to be run.