*: kv range to return current revision

This changes the behavior of KV's range and tx range to return
current revision rather than range revision. This makes populating
range response header easier.

integration/v3_grpc_test.go

@@ -1188,10 +1188,7 @@ func TestV3RangeRequest(t *testing.T) {
 			if resp.More != tt.wmores[j] {
 				t.Errorf("#%d.%d: bad more. got = %v, want = %v, ", i, j, resp.More, tt.wmores[j])
 			}
-			wrev := req.Revision
-			if wrev == 0 {
-				wrev = int64(len(tt.putKeys) + 1)
-			}
+			wrev := int64(len(tt.putKeys) + 1)
 			if resp.Header.Revision != wrev {
 				t.Errorf("#%d.%d: bad header revision. got = %d. want = %d", i, j, resp.Header.Revision, wrev)
 			}