Fix memory reusage bug with auth

Fixes #814

client_test.go

@@ -112,7 +112,7 @@ func TestClientURLAuth(t *testing.T) {
 	for up, expected := range cases {
 		req := AcquireRequest()
 		req.Header.SetMethod(MethodGet)
-		req.SetRequestURI("http://" + up + "example.com")
+		req.SetRequestURI("http://" + up + "example.com/foo/bar")
 		if err := c.Do(req, nil); err != nil {
 			t.Fatal(err)
 		}

uri.go

@@ -284,11 +284,11 @@ func (u *URI) parse(host, uri []byte, isTLS bool) {
 		host = host[n+1:]
 
 		if n := bytes.Index(auth, strColon); n >= 0 {
-			u.username = auth[:n]
-			u.password = auth[n+1:]
+			u.username = append(u.username[:0], auth[:n]...)
+			u.password = append(u.password[:0], auth[n+1:]...)
 		} else {
-			u.username = auth
-			u.password = auth[:0] // Make sure it's not nil
+			u.username = append(u.username[:0], auth...)
+			u.password = u.password[:0]
 		}
 	}