Spurious failure of file being used by another process on Windows

[alexcrichton]

http://buildbot.rust-lang.org/builders/auto-win-msvc-64-cargotest/builds/363/steps/test/logs/stdio
https://gist.github.com/alexcrichton/c1bb3e0c51d79cd13d59fed29059aea4

failures:

---- test_cargo_freshness::rebuild_tests_if_lib_changes stdout ----
    thread 'test_cargo_freshness::rebuild_tests_if_lib_changes' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 32, message: "The process cannot access the file because it is being used by another process." } }', C:\bot\slave\auto-win-msvc-64-cargotest\build\src\libcore\result.rs:785
note: Run with `RUST_BACKTRACE=1` for a backtrace.


failures:
    test_cargo_freshness::rebuild_tests_if_lib_changes

test result: FAILED. 633 passed; 1 failed; 0 ignored; 0 measured

Not.. entirely sure what's going on here.

[alexcrichton]

Cargo's no longer on buildbot, haven't seen this in awhile, so closing.