BUG: Fix failing python long behaviour and possible heisen bug

The priority error fixes np.float_(64) + python_long not working
anymore. The second change reformats the
PyArray_GetAttrString_SuppressException to avoid a possible
heisenbug decrefing an object before use.
Merge pull request #3453 from seberg/fix-enhanced-dtype-detection

BUG: Fix failing python long behaviour and possible heisen bug