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/libstd/sys/windows/ext.rs

@@ -39,6 +39,7 @@ pub trait AsRawHandle {
     fn as_raw_handle(&self) -> Handle;
 }
 
+#[allow(deprecated)]
 impl AsRawHandle for old_io::fs::File {
     fn as_raw_handle(&self) -> Handle {
         self.as_inner().handle()

src/libstd/sys/windows/process.rs

@@ -17,7 +17,7 @@ use hash::Hash;
 use libc::{pid_t, c_void};
 use libc;
 use mem;
-use old_io::fs::PathExtensions;
+#[allow(deprecated)] use old_io::fs::PathExtensions;
 use old_io::process::{ProcessExit, ExitStatus};
 use old_io::{IoResult, IoError};
 use old_io;