pandas series append will lost original name if new series name is different
#### Question about pandas

pandas series append will lost original name if new series name is different, probably can improve by adding an arg like retain_name=True?

```python
# Your code here, if applicable
s1 = pd.Series([1,2,3], name='A')
s2 = pd.Series([4,5,6], name='B')
s3 = pd.Series([7,8,9])
s4 = pd.Series([10,11,12], name='A')
print(s1.append(s2).name)
print(s1.append(s3).name)
print(s1.append(s4).name)
```
