PyQt5 (v5.7) backend - TypeError upon calling figure()

Windows 10
Python 3.5.2
PyQt 5.7
Matplotlib 1.5.1

The following code throws a TypeError when run. It appears that there's a connection error when trying to connect the NavigationToolbar2QT.message[str] signal to the FigureManagerQT._show_message() slot.

```
import matplotlib
matplotlib.use("Qt5Agg")
from matplotlib.pyplot import *

fig = figure()
show()
```
