add .get(), __bool__ and __nonzero__ to shared_ptr wrapper to allow testing if...

add .get(), __bool__ and __nonzero__ to shared_ptr wrapper to allow testing if the shared_ptr is valid

swig/boost_shared_ptr.i

@@ -14,6 +14,14 @@ namespace boost {
     shared_ptr();
     shared_ptr(T * p);
     T* operator->();
+    T* get();
+
+%pythoncode %{
+  def __bool__(self):
+     return self.get() is not None
+  __nonzero__=__bool__
+%}
+
   private:
     T * px;
     int pn;