This is a pure clean up except the last item which fixes a minor problem. I had wrote this patch a while ago (perhaps before 3.7.0 was released), and now revive my old patches.

I think that the general rule is that exceptions shouldn't be ignored blindly, except in case when we have no choice (like in destructors). ImportError and AttributeError are expected exceptions raised in PyImport_ImportModuleLevelObject and PyObject_GetAttrString when PYTHONBREAKPOINT points to non-existing name, all other exceptions mean exceptional situation or programming error. Note that exceptions raised when call the hook are not ignored.