auto merge of #5404 : bstrie/rust/decopy, r=pcwalton

Also turn `copy` into `.clone()` in much of run-pass.

src/libcore/str.rs

@@ -20,6 +20,7 @@
 use at_vec;
 use cast;
 use char;
+use clone::Clone;
 use cmp::{Equiv, TotalOrd, Ordering, Less, Equal, Greater};
 use libc;
 use option::{None, Option, Some};
@@ -2436,6 +2437,13 @@ impl OwnedStr for ~str {
     }
 }
 
+impl Clone for ~str {
+    #[inline(always)]
+    fn clone(&self) -> ~str {
+        self.to_str()  // hilarious
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use char;