Relax lifetime bounds on Reader/Writer impls for trait boxes

Cargo needs this to be able to instantiate `TerminfoTerminal<Box<Writer+'a>>`
for 'a other than 'static.

src/libstd/io/mod.rs

@@ -945,10 +945,16 @@ pub trait Reader {
     }
 }
 
+#[cfg(stage0)]
 impl Reader for Box<Reader+'static> {
     fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.read(buf) }
 }
 
+#[cfg(not(stage0))]
+impl<'a> Reader for Box<Reader+'a> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.read(buf) }
+}
+
 impl<'a> Reader for &'a mut Reader+'a {
     fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.read(buf) }
 }
@@ -1295,6 +1301,7 @@ pub trait Writer {
     }
 }
 
+#[cfg(stage0)]
 impl Writer for Box<Writer+'static> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.write(buf) }
@@ -1303,6 +1310,15 @@ impl Writer for Box<Writer+'static> {
     fn flush(&mut self) -> IoResult<()> { self.flush() }
 }
 
+#[cfg(not(stage0))]
+impl<'a> Writer for Box<Writer+'a> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.write(buf) }
+
+    #[inline]
+    fn flush(&mut self) -> IoResult<()> { self.flush() }
+}
+
 impl<'a> Writer for &'a mut Writer+'a {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.write(buf) }