Verify Rust source code formatting as part of the unit tests.
Verify Rust source code formatting as part of the unit tests.

Only do this is rustfmt is installed, which likely means don't run on Travis
CI.

stoklund/cretonne,sunfishcode/cretonne,stoklund/cretonne,stoklund/cretonne,sunfishcode/cretonne,sunfishcode/cretonne