Description:
PyQt5 apps crash on using qApp.quit() (or app_instance.quit())

Additional info:
* package version(s) : .*pyqt5.* 5.1 / 5.2

Steps to reproduce:
Use a simple PyQt5 app :


from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
if __name__ == '__main__':
app = QApplication(sys.argv)
btn = QPushButton('Test');
btn.clicked.connect(app.quit);

btn.show();
sys.exit(app.exec())

Click the test button and watch a segmentation fault, using gdb it dies in QWidget::~QWidget();
Writing the same test app in C++ doesn't result in a crash.