Make Python builtin types hashable by default

Default hash is the underlying C/C++ pointer.
This matches up with testing for equivalence (Py_EQ in SwigPyObject_richcompare)
which compares the pointers.

Examples/test-suite/python/python_builtin_runme.py

@@ -1,6 +1,17 @@
 from python_builtin import *
 
 if is_python_builtin():
+  # Test 0 for default tp_hash
+  vs = ValueStruct(1234)
+  h = hash(vs)
+  d = dict()
+  d[h] = "hi"
+  if h not in d:
+    raise RuntimeError("h should be in d")
+  h2 = hash(ValueStruct.inout(vs))
+  if h != h2:
+    raise RuntimeError("default tp_hash not working")
+
   # Test 1 for tp_hash
   if hash(SimpleValue(222)) != 222:
     raise RuntimeError("tp_hash not working")

Examples/test-suite/python_builtin.i

@@ -10,6 +10,17 @@ bool is_python_builtin() { return false; }
 #endif
 %}
 
+// Test 0 for default tp_hash
+%inline %{
+struct ValueStruct {
+  int value;
+  ValueStruct(int value) : value(value) {}
+  static ValueStruct *inout(ValueStruct *v) {
+    return v;
+  }
+};
+%}
+
 // Test 1 for tp_hash
 #if defined(SWIGPYTHON_BUILTIN)
 %feature("python:tp_hash") SimpleValue "SimpleValueHashFunction"
@@ -19,9 +30,6 @@ bool is_python_builtin() { return false; }
 struct SimpleValue {
   int value;
   SimpleValue(int value) : value(value) {}
-  static SimpleValue *inout(SimpleValue *sv) {
-    return sv;
-  }
 };
 %}