Fix pybind11 issues. (#1248)

* Fix pybind11 issues.

* Retract suspicious fix.

* Address comments.

python/schedule.hpp

@@ -18,6 +18,7 @@ struct schedule_shim_base {
     schedule_shim_base() = default;
     schedule_shim_base(const schedule_shim_base&) = delete;
     schedule_shim_base& operator=(schedule_shim_base&) = delete;
+    virtual ~schedule_shim_base() {}
 
     virtual arb::schedule schedule() const = 0;
 };

python/simulation.cpp

@@ -107,7 +107,7 @@ public:
     }
 
     py::object spikes() const {
-        return py::array_t<arb::spike>({spike_record_.size()}, spike_record_.data());
+        return py::array_t<arb::spike>(py::ssize_t(spike_record_.size()), spike_record_.data());
     }
 
     py::list get_probe_metadata(arb::cell_member_type probe_id) const {