Remove impl Seek for MemWriterFakeStream.

Its seekability wasn’t being used, and so in light of the changes made
in rust-lang/rust#15915 it should be removed, rather than switching from
the now-unseekable ``MemWriter`` to the new ``SeekableMemWriter``.

This necessitated adding the ``get_ref`` method which was added to
``MemWriter`` at some point.

Author: chris-morgan

src/http/memstream.rs

@@ -8,6 +8,11 @@ struct MemWriterFakeStream(MemWriter);
 
 impl MemWriterFakeStream {
     pub fn new() -> MemWriterFakeStream { MemWriterFakeStream(MemWriter::new()) }
+
+    pub fn get_ref(&self) -> &[u8] {
+        let &MemWriterFakeStream(ref s) = self;
+        s.get_ref()
+    }
 }
 
 impl Writer for MemWriterFakeStream {
@@ -22,18 +27,6 @@ impl Writer for MemWriterFakeStream {
     }
 }
 
-impl Seek for MemWriterFakeStream {
-    fn tell(&self) -> IoResult<u64> {
-        let &MemWriterFakeStream(ref s) = self;
-        s.tell()
-    }
-
-    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
-        let &MemWriterFakeStream(ref mut s) = self;
-        s.seek(pos, style)
-    }
-}
-
 impl Reader for MemWriterFakeStream {
     fn read(&mut self, _buf: &mut [u8]) -> IoResult<uint> {
         fail!("Uh oh, you didn't aught to call MemWriterFakeStream.read()!")
@@ -82,12 +75,12 @@ mod test {
     #[test]
     fn test_mem_writer_fake_stream() {
         let mut writer = MemWriterFakeStream::new();
-        assert_eq!(writer.tell(),              Ok(0));
+        assert_eq!(writer.get_ref(),           &[]);
         assert_eq!(writer.write([0]),          Ok(()));
-        assert_eq!(writer.tell(),              Ok(1));
+        assert_eq!(writer.get_ref(),           &[0]);
         assert_eq!(writer.write([1, 2, 3]),    Ok(()));
         assert_eq!(writer.write([4, 5, 6, 7]), Ok(()));
-        assert_eq!(writer.tell(),              Ok(8));
+        assert_eq!(writer.get_ref(),           &[0, 1, 2, 3, 4, 5, 6, 7]);
     }
 
     #[test]