Fix DirEntryInner::is_same_file at a mountpoint (#333)

If a direntry comes from a mountpoint's parent, then its ino will be the
ino of the underlying directory, not the mounted file system's root
directory.  So ignore the direntry's ino, and just look at the ino in
its metadata.

Fixes #330

Author: asomers

cap-primitives/src/rustix/fs/dir_entry_inner.rs

@@ -69,7 +69,8 @@ impl DirEntryInner {
 
     #[inline]
     pub(crate) fn is_same_file(&self, metadata: &Metadata) -> io::Result<bool> {
-        Ok(self.ino() == metadata.ino() && self.metadata()?.dev() == metadata.dev())
+        let self_md = self.metadata()?;
+        Ok(self_md.ino() == metadata.ino() && self_md.dev() == metadata.dev())
     }
 
     fn file_name_bytes(&self) -> &OsStr {