Update Python tests to not use flatstaticmethod access

Use Python class staticmethod syntax to access C++ static member functions,
such as Klass.memberfunction, instead of Klass_memberfunction.
Examples and test-suite changes in preparation for issue #2137.

Examples/test-suite/python/overload_template_runme.py

@@ -140,6 +140,6 @@ if (nsoverload() != 1050):
     raise RuntimeError(("nsoverload(const char *)"))
 
 
-A_foo(1)
+A.foo(1)
 b = B()
 b.foo(1)