 Vector updated, +:, and :+ fall back to slow performance... 2.10.1 binary compat.

We have to make the change for #6150 binary compatible with 2.10.0.

```
     [java]  * class scala.collection.immutable.Vector#VectorReusableCBF does not have a
     [java]    correspondent in new version
     [java]  * class scala.collection.generic.GenTraversableFactory#ReusableCBF does not
     [java]    have a correspondent in new version
```