Backout the original 'fix' to 1721309 which had no effect.

Different versions of Berkeley DB handle this differently.
The comments and bug report should have the details.  Memory is allocated
in 4.4 (and presumably earlier), but not in 4.5.  Thus
4.5 has the free error, but not earlier versions.

Mostly update comments, plus make the free conditional.

Modules/_bsddb.c

@@ -1695,6 +1695,7 @@ DB_get_both(DBObject* self, PyObject* args, PyObject* kwargs)
     PyObject* dataobj;
     PyObject* retval = NULL;
     DBT key, data;
+    void *orig_data;
     DB_TXN *txn = NULL;
     static char* kwnames[] = { "key", "data", "txn", "flags", NULL };
 
@@ -1706,7 +1707,6 @@ DB_get_both(DBObject* self, PyObject* args, PyObject* kwargs)
     CHECK_DB_NOT_CLOSED(self);
     if (!make_key_dbt(self, keyobj, &key, NULL))
         return NULL;
-    CLEAR_DBT(data);
     if ( !make_dbt(dataobj, &data) ||
          !checkTxnObj(txnobj, &txn) )
     {
@@ -1715,13 +1715,12 @@ DB_get_both(DBObject* self, PyObject* args, PyObject* kwargs)
     }
 
     flags |= DB_GET_BOTH;
+    orig_data = data.data;
 
     if (CHECK_DBFLAG(self, DB_THREAD)) {
         /* Tell BerkeleyDB to malloc the return value (thread safe) */
+        /* XXX(nnorwitz): At least 4.4.20 and 4.5.20 require this flag. */
         data.flags = DB_DBT_MALLOC;
-        /* TODO: Is this flag needed?  We're passing a data object that should
-                 match what's in the DB, so there should be no need to malloc.
-                 We run the risk of freeing something twice!  Check this. */
     }
 
     MYDB_BEGIN_ALLOW_THREADS;
@@ -1735,8 +1734,13 @@ DB_get_both(DBObject* self, PyObject* args, PyObject* kwargs)
         retval = Py_None;
     }
     else if (!err) {
+        /* XXX(nnorwitz): can we do: retval = dataobj; Py_INCREF(retval); */
         retval = PyString_FromStringAndSize((char*)data.data, data.size);
-        FREE_DBT(data); /* Only if retrieval was successful */
+
+        /* Even though the flags require DB_DBT_MALLOC, data is not always
+           allocated.  4.4: allocated, 4.5: *not* allocated. :-( */
+        if (data.data != orig_data)
+            FREE_DBT(data);
     }
 
     FREE_DBT(key);