canonical-path: CanonicalPath::join() should canonicalize.

[sethfowler]

Nice library! It's quite useful.

I did run into an issue, though. My expectation was that this pseudo-code should work:

let ref_path = CanonicalPath::new("/foo/bar/").unwrap();
let relative_path = Path::new("../baz");
let abs_path = ref_path.join(&relative_path).expect("This should succeed!");
assert_eq!(CanonicalPath::new("/foo/baz"), abs_path);

In reality, the call to join() fails. This happens because relative_path contains ../ and CanonicalPath::join() just concatenates the two paths and calls CanonicalPathBuf::new(). Since CanonicalPathBuf::new() returns Err if the path is not already canonical, CanonicalPath::join() does as well. If CanonicalPath::join() called CanonicalPathBuf::canonicalize() instead, then this code would work as expected.

For now, I'm using this approach as a workaround:

let abs_path = CanonicalPathBuf::canonicalize(ref_path.as_path().join(&relative_path));