DEL key not working on OS X (10.11.3) after the switch to curtsies 2.2

After upgrading to v0.15 I noticed my DEL key wasn't working anymore within the bpython session. I git bisected it down to this commit:

```
commit 3cfac865c915269ba593c1e9ea1442c6b6f6f7d0
Author: Thomas Ballinger <thomasballinger@gmail.com>
Date:   Tue Feb 17 19:08:55 2015 -0500

    switch to curtsies v2.2, fmtstrs unicode
```
