std: Deprecate std::old_io::fs

This commit deprecates the majority of std::old_io::fs in favor of std::fs and
its new functionality. Some functions remain non-deprecated but are now behind a
feature gate called `old_fs`. These functions will be deprecated once
suitable replacements have been implemented.

The compiler has been migrated to new `std::fs` and `std::path` APIs where
appropriate as part of this change.

src/libserialize/serialize.rs

@@ -15,6 +15,7 @@ Core encoding and decoding interfaces.
 */
 
 use std::old_path;
+use std::path;
 use std::rc::Rc;
 use std::cell::{Cell, RefCell};
 use std::sync::Arc;
@@ -564,6 +565,19 @@ impl Decodable for old_path::windows::Path {
     }
 }
 
+impl Encodable for path::PathBuf {
+    fn encode<S: Encoder>(&self, e: &mut S) -> Result<(), S::Error> {
+        self.to_str().unwrap().encode(e)
+    }
+}
+
+impl Decodable for path::PathBuf {
+    fn decode<D: Decoder>(d: &mut D) -> Result<path::PathBuf, D::Error> {
+        let bytes: String = try!(Decodable::decode(d));
+        Ok(path::PathBuf::new(&bytes))
+    }
+}
+
 impl<T: Encodable + Copy> Encodable for Cell<T> {
     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
         self.get().encode(s)