librustc: Implement explicit self for Add and Index; add a hack in the borrow checker to support this. r=nmatsakis

src/libcore/str.rs

@@ -2107,12 +2107,21 @@ impl ~str: Trimmable {
 
 #[cfg(notest)]
 pub mod traits {
+    #[cfg(stage0)]
     impl ~str : Add<&str,~str> {
         #[inline(always)]
         pure fn add(rhs: & &self/str) -> ~str {
             append(copy self, (*rhs))
         }
     }
+    #[cfg(stage1)]
+    #[cfg(stage2)]
+    impl ~str : Add<&str,~str> {
+        #[inline(always)]
+        pure fn add(&self, rhs: & &self/str) -> ~str {
+            append(copy *self, (*rhs))
+        }
+    }
 }
 
 #[cfg(test)]