BUG: retain writeable flag when indexing subclasses

The `d[True]` raises a Warning that causes the test to fail.
```
/home/charris/.local/lib/python2.7/site-packages/numpy/core/records.py:459: DeprecationWarning: using a boolean instead of an integer will result in an error in the future
```
The easy fix is to remove the check or use an integer.