Fragment animations are not being saved across configuration changes

As per comment #5 in issue #25994:

The problem here is not that the state isn't saved and restored, the problem is how the BackStackRecord is rebuilt.  The ops themselves do save and restore the state, the problem is in BackStackRecord#addOp.

    void addOp(Op op) {
        if (mHead == null) {
            mHead = mTail = op;
        } else {
            op.prev = mTail;
            mTail.next = op;
            mTail = op;
        }
        op.enterAnim = mEnterAnim;
        op.exitAnim = mExitAnim;
        op.popEnterAnim = mPopEnterAnim;
        op.popExitAnim = mPopExitAnim;
        mNumOp++;
    }

The enter, exit, popEnter and popExit animations are overwritten with whatever is currently in the record, which during the restoration process these are 0 so the values which were saved in the ops is lost.

Change-Id: I095cc7ff4ae65581d728f34217fb873ad2f0c574