Refactor [module|capi]_aq_chain

* Usual tabs/spaces/indent stuff
* Make use of the fact that __new__ ensures that self->obj is never NULL
* Fix memory leak when PyObject_GetAttr(self, py__parent__) raised
  something else then AttributeError. Before 'result' was leaking.
* The 'err:' section returned 'result' in case of erros. Due to the decref
  before 'result' became an invalid pointer. Returning this pointer
  would have let to a segfault. The proper way to signal an error is by
  returning a NULL pointer. As it is done now.
* Prevent segfault if the return value of
  PyObject_GetAttr(self, py__parent__) had an refcount of 1.
  In that case it Py_DECREF came too early and an access of this pointer
  later would have lead to segfault. Now the reference is kept alive
  until the end of the function. Yes this complicated the other
  assignments to self a bit.

src/Acquisition/_Acquisition.c

@@ -1845,70 +1845,73 @@ module_aq_inner(PyObject *ignored, PyObject *self)
 static PyObject *
 capi_aq_chain(PyObject *self, int containment)
 {
-  PyObject *result, *v, *tb;
+    PyObject *result;
 
-  UNLESS (result=PyList_New(0)) return NULL;
+    /* This allows Py_XDECREF at the end.
+     * Needed, because the result of PyObject_GetAttr(self, py__parent__) must
+     * be kept alive until not needed anymore. It could be that the refcount of
+     * its return value is 1 => calling Py_DECREF too early leads to segfault.
+     */
+    Py_INCREF(self);
 
-  while (1)
-    {
-      if (isWrapper(self))
-	{
-	  if (WRAPPER(self)->obj)
-	    {
-	      if (containment)
-		while (WRAPPER(self)->obj && isWrapper(WRAPPER(self)->obj))
-		  self=WRAPPER(self)->obj;
-	      if (PyList_Append(result,OBJECT(self)) < 0)
-		goto err;
-	    }
-	  if (WRAPPER(self)->container) 
-	    {
-	      self=WRAPPER(self)->container;
-	      continue;
-	    }
-	}
-      else
-        {
-          if (PyList_Append(result, self) < 0)
-            goto err;
+    if ((result = PyList_New(0)) == NULL) {
+        return NULL;
+    }
+
+    while (1) {
+        if (isWrapper(self)) {
+            if (containment) {
+                while (isWrapper(WRAPPER(self)->obj)) {
+                    ASSIGN(self, WRAPPER(self)->obj);
+                    Py_INCREF(self);
+                }
+            }
+
+            if (PyList_Append(result, OBJECT(self)) < 0) {
+                goto err;
+            }
 
-          if ((self=PyObject_GetAttr(self, py__parent__)))
-            {
-              Py_DECREF(self); /* We don't need our own reference. */
-              if (self!=Py_None)
+            if (WRAPPER(self)->container) {
+                ASSIGN(self, WRAPPER(self)->container);
+                Py_INCREF(self);
                 continue;
             }
-          else
-            {
-              PyErr_Fetch(&self,&v,&tb);
-              if (self && (self != PyExc_AttributeError))
-                {
-                  PyErr_Restore(self,v,tb);
-                  return NULL;
+        } else {
+            if (PyList_Append(result, self) < 0) {
+                goto err;
+            }
+
+            ASSIGN(self, PyObject_GetAttr(self, py__parent__));
+            if (self) {
+                if (self != Py_None) {
+                    continue;
                 }
-              Py_XDECREF(self); Py_XDECREF(v); Py_XDECREF(tb);
+            } else if (!swallow_attribute_error()) {
+                goto err;
             }
         }
-
-      break;
+        break;
     }
 
-  return result;
+    Py_XDECREF(self);
+    return result;
 err:
-  Py_DECREF(result);
-  return result;
+    Py_XDECREF(self);
+    Py_DECREF(result);
+    return NULL;
 }
 
 static PyObject *
 module_aq_chain(PyObject *ignored, PyObject *args)
 {
-  PyObject *self;
-  int containment=0;
+    PyObject *self;
+    int containment = 0;
 
-  UNLESS (PyArg_ParseTuple(args, "O|i", &self, &containment))
-    return NULL;
+    if (!PyArg_ParseTuple(args, "O|i", &self, &containment)) {
+        return NULL;
+    }
 
-  return capi_aq_chain(self, containment);
+    return capi_aq_chain(self, containment);
 }
 
 static PyObject *