std: Rename Writer::write to Writer::write_all

In preparation for upcoming changes to the `Writer` trait (soon to be called
`Write`) this commit renames the current `write` method to `write_all` to match
the semantics of the upcoming `write_all` method. The `write` method will be
repurposed to return a `usize` indicating how much data was written which
differs from the current `write` semantics. In order to head off as much
unintended breakage as possible, the method is being deprecated now in favor of
a new name.

[breaking-change]

src/libstd/old_io/net/pipe.rs

@@ -142,7 +142,7 @@ impl Reader for UnixStream {
 }
 
 impl Writer for UnixStream {
-    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+    fn write_all(&mut self, buf: &[u8]) -> IoResult<()> {
         self.inner.write(buf)
     }
 }