ENH: How about "cannot reindex from an index with duplicate values"?
#### Is your feature request related to a problem?

I spent quite a bit of time trying to figure out what this message means:

`*** ValueError: cannot reindex from a duplicate axis`


#### Describe the solution you'd like

It would have been much easier for me to figure out what I was doing wrong with the message:

`*** ValueError: cannot reindex from an index with duplicate values`
