This fixes lints for tests/tests.rs and adds a test for rename. The new
rename test is based on the rename_no_replace tests. There are two
discrepancies between Linux and Redox but I'm not sure if they matter. I
added a note to those tests.
There are two fixed lints of note.
* assert_cmd deprecated Command::cargo_bin in favor of a compile time
checked macro.
* The mode literals were wrong: 0666 instead of 0o666. 0o is the prefix
for octal literals.
Josh Megnauth
2b8ea938ea