Fix broken target scrape error propagation.

retrieval/target.go

@@ -138,7 +138,8 @@ func (t *target) Scrape(earliest time.Time, results chan format.Result) (err err
 			done <- true
 		}()
 
-		resp, err := http.Get(t.Address())
+		var resp *http.Response // Don't shadow "err" from the enclosing function.
+		resp, err = http.Get(t.Address())
 		if err != nil {
 			return
 		}