[Go] Fix member variables in base classes to handle CWRAP_NATURAL_VAR

correctly.  Add a test case for the problem.

Fixes #339.

Examples/test-suite/go/inherit_member_runme.go

@@ -0,0 +1,15 @@
+package main
+
+import wrap "./inherit_member"
+
+func main() {
+	s := wrap.NewChild()
+	s.SetPvar("p")
+	s.SetCvar("c")
+	if s.GetPvar() != "p" {
+		panic(s.GetPvar())
+	}
+	if s.GetCvar() != "c" {
+		panic(s.GetCvar())
+	}
+}