Stabilize std::path

This commit stabilizes essentially all of the new `std::path` API. The
API itself is changed in a couple of ways (which brings it in closer
alignment with the RFC):

* `.` components are now normalized away, unless they appear at the
  start of a path. This in turn effects the semantics of e.g. asking for
  the file name of `foo/` or `foo/.`, both of which yield `Some("foo")`
  now. This semantics is what the original RFC specified, and is also
  desirable given early experience rolling out the new API.

* The `parent` function now succeeds if, and only if, the path has at
  least one non-root/prefix component. This change affects `pop` as
  well.

* The `Prefix` component now involves a separate `PrefixComponent`
  struct, to better allow for keeping both parsed and unparsed prefix data.

In addition, the `old_path` module is now deprecated.

Closes #23264

[breaking-change]

1 files changed, 2 insertions, 12 deletions

diff --git a/src/libstd/fs/mod.rs b/src/libstd/fs/mod.rs
index 9f9163eb9e6..d8ee62ac239 100644
--- a/src/libstd/fs/mod.rs
+++ b/src/libstd/fs/mod.rs
@@ -571,18 +571,8 @@ pub fn create_dir<P: AsPath + ?Sized>(path: &P) -> io::Result<()> {
 pub fn create_dir_all<P: AsPath + ?Sized>(path: &P) -> io::Result<()> {
     let path = path.as_path();
     if path.is_dir() { return Ok(()) }
-    match path.parent() {
-        Some(p) if p != path => try!(create_dir_all(p)),
-        _ => {}
-    }
-    // If the file name of the given `path` is blank then the creation of the
-    // parent directory will have taken care of the whole path for us, so we're
-    // good to go.
-    if path.file_name().is_none() {
-        Ok(())
-    } else {
-        create_dir(path)
-    }
+    if let Some(p) = path.parent() { try!(create_dir_all(p)) }
+    create_dir(path)
 }
 
 /// Remove an existing, empty directory