Many Bundle properties are wrong on Windows after swift-foundation re-coring

[jakepetroules]

For example, executablePath is implemented like so:

    open var executablePath: String? {
        return executableURL?.path
    }

This will result in it having an incorrect leading slash (like /C:/foo/bar/baz); instead it should use withUnsafeFileSystemRepresentation.

[jakepetroules]

This also applies to free functions like NSTemporaryDirectory and NSHomeDirectory.